1 This is tar.info, produced by makeinfo version 4.13 from tar.texi.
3 This manual is for GNU `tar' (version 1.24, 24 October 2010), which
4 creates and extracts files from archives.
6 Copyright (C) 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001, 2003,
7 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
9 Permission is granted to copy, distribute and/or modify this
10 document under the terms of the GNU Free Documentation License,
11 Version 1.3 or any later version published by the Free Software
12 Foundation; with no Invariant Sections, with the Front-Cover Texts
13 being "A GNU Manual", and with the Back-Cover Texts as in (a)
14 below. A copy of the license is included in the section entitled
15 "GNU Free Documentation License".
17 (a) The FSF's Back-Cover Text is: "You have the freedom to copy
18 and modify this GNU manual. Buying copies from the FSF supports
19 it in developing GNU and promoting software freedom."
21 INFO-DIR-SECTION Archiving
23 * Tar: (tar). Making tape (or disk) archives.
26 INFO-DIR-SECTION Individual utilities
28 * tar: (tar)tar invocation. Invoking GNU `tar'.
32 File: tar.info, Node: Top, Next: Introduction, Up: (dir)
34 GNU tar: an archiver tool
35 *************************
37 This manual is for GNU `tar' (version 1.24, 24 October 2010), which
38 creates and extracts files from archives.
40 Copyright (C) 1992, 1994, 1995, 1996, 1997, 1999, 2000, 2001, 2003,
41 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
43 Permission is granted to copy, distribute and/or modify this
44 document under the terms of the GNU Free Documentation License,
45 Version 1.3 or any later version published by the Free Software
46 Foundation; with no Invariant Sections, with the Front-Cover Texts
47 being "A GNU Manual", and with the Back-Cover Texts as in (a)
48 below. A copy of the license is included in the section entitled
49 "GNU Free Documentation License".
51 (a) The FSF's Back-Cover Text is: "You have the freedom to copy
52 and modify this GNU manual. Buying copies from the FSF supports
53 it in developing GNU and promoting software freedom."
55 The first part of this master menu lists the major nodes in this Info
56 document. The rest of the menu lists all the lower level nodes.
66 * Date input formats::
69 * Reliability and security::
74 * Configuring Help Summary::
75 * Fixing Snapshot Files::
78 * Free Software Needs Free Documentation::
79 * GNU Free Documentation License::
80 * Index of Command Line Options::
83 --- The Detailed Node Listing ---
87 * Book Contents:: What this Book Contains
88 * Definitions:: Some Definitions
89 * What tar Does:: What `tar' Does
90 * Naming tar Archives:: How `tar' Archives are Named
91 * Authors:: GNU `tar' Authors
92 * Reports:: Reporting bugs or suggestions
94 Tutorial Introduction to `tar'
97 * stylistic conventions::
98 * basic tar options:: Basic `tar' Operations and Options
99 * frequent operations::
100 * Two Frequent Options::
101 * create:: How to Create Archives
102 * list:: How to List Archives
103 * extract:: How to Extract Members from an Archive
106 Two Frequently Used Options
112 How to Create Archives
114 * prepare for examples::
115 * Creating the archive::
124 How to Extract Members from an Archive
126 * extracting archives::
129 * extracting untrusted archives::
135 * using tar options::
145 The Three Option Styles
147 * Long Options:: Long Option Style
148 * Short Options:: Short Option Style
149 * Old Options:: Old Option Style
150 * Mixing:: Mixing Option Styles
154 * Operation Summary::
156 * Short Option Summary::
168 Advanced GNU `tar' Operations
177 How to Add Files to Existing Archives: `--append'
179 * appending files:: Appending Files to an Archive
186 Options Used by `--create'
188 * override:: Overriding File Metadata.
189 * Ignore Failed Read::
191 Options Used by `--extract'
193 * Reading:: Options to Help Read Archives
194 * Writing:: Changing How `tar' Writes Files
195 * Scarce:: Coping with Scarce Resources
197 Options to Help Read Archives
199 * read full records::
202 Changing How `tar' Writes Files
204 * Dealing with Old Files::
205 * Overwrite Old Files::
210 * Data Modification Times::
211 * Setting Access Permissions::
212 * Directory Modification Times and Permissions::
213 * Writing to Standard Output::
214 * Writing to an External Program::
217 Coping with Scarce Resources
222 Performing Backups and Restoring Files
224 * Full Dumps:: Using `tar' to Perform Full Dumps
225 * Incremental Dumps:: Using `tar' to Perform Incremental Dumps
226 * Backup Levels:: Levels of Backups
227 * Backup Parameters:: Setting Parameters for Backups and Restoration
228 * Scripted Backups:: Using the Backup Scripts
229 * Scripted Restoration:: Using the Restore Script
231 Setting Parameters for Backups and Restoration
233 * General-Purpose Variables::
234 * Magnetic Tape Control::
236 * backup-specs example:: An Example Text of `Backup-specs'
238 Choosing Files and Names for `tar'
240 * file:: Choosing the Archive's Name
241 * Selecting Archive Members::
242 * files:: Reading Names from a File
243 * exclude:: Excluding Some Files
244 * wildcards:: Wildcards Patterns and Matching
245 * quoting styles:: Ways of Quoting Special Characters in Names
246 * transform:: Modifying File and Member Names
247 * after:: Operating Only on New Files
248 * recurse:: Descending into Directories
249 * one:: Crossing File System Boundaries
251 Reading Names from a File
257 * problems with exclude::
259 Wildcards Patterns and Matching
261 * controlling pattern-matching::
263 Crossing File System Boundaries
265 * directory:: Changing Directory
266 * absolute:: Absolute File Names
270 * General date syntax:: Common rules.
271 * Calendar date items:: 19 Dec 1994.
272 * Time of day items:: 9:20pm.
273 * Time zone items:: EST, PDT, GMT.
274 * Day of week items:: Monday and others.
275 * Relative items in date strings:: next tuesday, 2 years ago.
276 * Pure numbers in date strings:: 19931219, 1440.
277 * Seconds since the Epoch:: @1078100502.
278 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
279 * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al.
281 Controlling the Archive Format
283 * Compression:: Using Less Space through Compression
284 * Attributes:: Handling File Attributes
285 * Portability:: Making `tar' Archives More Portable
286 * cpio:: Comparison of `tar' and `cpio'
288 Using Less Space through Compression
290 * gzip:: Creating and Reading Compressed Archives
291 * sparse:: Archiving Sparse Files
293 Creating and Reading Compressed Archives
295 * lbzip2:: Using lbzip2 with GNU `tar'.
297 Making `tar' Archives More Portable
299 * Portable Names:: Portable Names
300 * dereference:: Symbolic Links
301 * hard links:: Hard Links
302 * old:: Old V7 Archives
303 * ustar:: Ustar Archives
304 * gnu:: GNU and old GNU format archives.
305 * posix:: POSIX archives
306 * Checksumming:: Checksumming Problems
307 * Large or Negative Values:: Large files, negative time stamps, etc.
308 * Other Tars:: How to Extract GNU-Specific Data Using
309 Other `tar' Implementations
311 GNU `tar' and POSIX `tar'
313 * PAX keywords:: Controlling Extended Header Keywords.
315 How to Extract GNU-Specific Data Using Other `tar' Implementations
317 * Split Recovery:: Members Split Between Volumes
318 * Sparse Recovery:: Sparse Members
320 Tapes and Other Archive Media
322 * Device:: Device selection and switching
323 * Remote Tape Server::
324 * Common Problems and Solutions::
325 * Blocking:: Blocking
326 * Many:: Many archives on one tape
327 * Using Multiple Tapes:: Using Multiple Tapes
328 * label:: Including a Label in the Archive
334 * Format Variations:: Format Variations
335 * Blocking Factor:: The Blocking Factor of an Archive
337 Many Archives on One Tape
339 * Tape Positioning:: Tape Positions and Tape Marks
340 * mt:: The `mt' Utility
344 * Multi-Volume Archives:: Archives Longer than One Tape or Disk
345 * Tape Files:: Tape Files
346 * Tarcat:: Concatenate Volumes into a Single Archive
351 * Standard:: Basic Tar Format
352 * Extensions:: GNU Extensions to the Archive Format
353 * Sparse Formats:: Storing Sparse Files
360 * PAX 0:: PAX Format, Versions 0.0 and 0.1
361 * PAX 1:: PAX Format, Version 1.0
365 * Generate Mode:: File Generation Mode.
366 * Status Mode:: File Status Mode.
367 * Exec Mode:: Synchronous Execution mode.
371 * GNU Free Documentation License:: License for copying this manual
374 File: tar.info, Node: Introduction, Next: Tutorial, Prev: Top, Up: Top
379 GNU `tar' creates and manipulates "archives" which are actually
380 collections of many other files; the program provides users with an
381 organized and systematic method for controlling a large amount of data.
382 The name "tar" originally came from the phrase "Tape ARchive", but
383 archives need not (and these days, typically do not) reside on tapes.
387 * Book Contents:: What this Book Contains
388 * Definitions:: Some Definitions
389 * What tar Does:: What `tar' Does
390 * Naming tar Archives:: How `tar' Archives are Named
391 * Authors:: GNU `tar' Authors
392 * Reports:: Reporting bugs or suggestions
395 File: tar.info, Node: Book Contents, Next: Definitions, Up: Introduction
397 1.1 What this Book Contains
398 ===========================
400 The first part of this chapter introduces you to various terms that will
401 recur throughout the book. It also tells you who has worked on GNU
402 `tar' and its documentation, and where you should send bug reports or
405 The second chapter is a tutorial (*note Tutorial::) which provides a
406 gentle introduction for people who are new to using `tar'. It is meant
407 to be self-contained, not requiring any reading from subsequent
408 chapters to make sense. It moves from topic to topic in a logical,
409 progressive order, building on information already explained.
411 Although the tutorial is paced and structured to allow beginners to
412 learn how to use `tar', it is not intended solely for beginners. The
413 tutorial explains how to use the three most frequently used operations
414 (`create', `list', and `extract') as well as two frequently used
415 options (`file' and `verbose'). The other chapters do not refer to the
416 tutorial frequently; however, if a section discusses something which is
417 a complex variant of a basic concept, there may be a cross-reference to
418 that basic concept. (The entire book, including the tutorial, assumes
419 that the reader understands some basic concepts of using a Unix-type
420 operating system; *note Tutorial::.)
422 The third chapter presents the remaining five operations, and
423 information about using `tar' options and option syntax.
425 The other chapters are meant to be used as a reference. Each chapter
426 presents everything that needs to be said about a specific topic.
428 One of the chapters (*note Date input formats::) exists in its
429 entirety in other GNU manuals, and is mostly self-contained. In
430 addition, one section of this manual (*note Standard::) contains a big
431 quote which is taken directly from `tar' sources.
433 In general, we give both long and short (abbreviated) option names
434 at least once in each section where the relevant option is covered, so
435 that novice readers will become familiar with both styles. (A few
436 options have no short versions, and the relevant sections will indicate
440 File: tar.info, Node: Definitions, Next: What tar Does, Prev: Book Contents, Up: Introduction
445 The `tar' program is used to create and manipulate `tar' archives. An
446 "archive" is a single file which contains the contents of many files,
447 while still identifying the names of the files, their owner(s), and so
448 forth. (In addition, archives record access permissions, user and
449 group, size in bytes, and data modification time. Some archives also
450 record the file names in each archived directory, as well as other file
451 and directory information.) You can use `tar' to "create" a new
452 archive in a specified directory.
454 The files inside an archive are called "members". Within this
455 manual, we use the term "file" to refer only to files accessible in the
456 normal ways (by `ls', `cat', and so forth), and the term "member" to
457 refer only to the members of an archive. Similarly, a "file name" is
458 the name of a file, as it resides in the file system, and a "member
459 name" is the name of an archive member within the archive.
461 The term "extraction" refers to the process of copying an archive
462 member (or multiple members) into a file in the file system. Extracting
463 all the members of an archive is often called "extracting the archive".
464 The term "unpack" can also be used to refer to the extraction of many
465 or all the members of an archive. Extracting an archive does not
466 destroy the archive's structure, just as creating an archive does not
467 destroy the copies of the files that exist outside of the archive. You
468 may also "list" the members in a given archive (this is often thought
469 of as "printing" them to the standard output, or the command line), or
470 "append" members to a pre-existing archive. All of these operations
471 can be performed using `tar'.
474 File: tar.info, Node: What tar Does, Next: Naming tar Archives, Prev: Definitions, Up: Introduction
479 The `tar' program provides the ability to create `tar' archives, as
480 well as various other kinds of manipulation. For example, you can use
481 `tar' on previously created archives to extract files, to store
482 additional files, or to update or list files which were already stored.
484 Initially, `tar' archives were used to store files conveniently on
485 magnetic tape. The name `tar' comes from this use; it stands for
486 `t'ape `ar'chiver. Despite the utility's name, `tar' can direct its
487 output to available devices, files, or other programs (using pipes).
488 `tar' may even access remote devices or files (as archives).
490 You can use `tar' archives in many ways. We want to stress a few of
491 them: storage, backup, and transportation.
494 Often, `tar' archives are used to store related files for
495 convenient file transfer over a network. For example, the GNU
496 Project distributes its software bundled into `tar' archives, so
497 that all the files relating to a particular program (or set of
498 related programs) can be transferred as a single unit.
500 A magnetic tape can store several files in sequence. However, the
501 tape has no names for these files; it only knows their relative
502 position on the tape. One way to store several files on one tape
503 and retain their names is by creating a `tar' archive. Even when
504 the basic transfer mechanism can keep track of names, as FTP can,
505 the nuisance of handling multiple files, directories, and multiple
506 links makes `tar' archives useful.
508 Archive files are also used for long-term storage. You can think
509 of this as transportation from the present into the future. (It
510 is a science-fiction idiom that you can move through time as well
511 as in space; the idea here is that `tar' can be used to move
512 archives in all dimensions, even time!)
515 Because the archive created by `tar' is capable of preserving file
516 information and directory structure, `tar' is commonly used for
517 performing full and incremental backups of disks. A backup puts a
518 collection of files (possibly pertaining to many users and
519 projects) together on a disk or a tape. This guards against
520 accidental destruction of the information in those files. GNU
521 `tar' has special features that allow it to be used to make
522 incremental and full dumps of all the files in a file system.
525 You can create an archive on one system, transfer it to another
526 system, and extract the contents there. This allows you to
527 transport a group of files from one system to another.
530 File: tar.info, Node: Naming tar Archives, Next: Authors, Prev: What tar Does, Up: Introduction
532 1.4 How `tar' Archives are Named
533 ================================
535 Conventionally, `tar' archives are given names ending with `.tar'.
536 This is not necessary for `tar' to operate properly, but this manual
537 follows that convention in order to accustom readers to it and to make
540 Often, people refer to `tar' archives as "`tar' files," and archive
541 members as "files" or "entries". For people familiar with the
542 operation of `tar', this causes no difficulty. However, in this
543 manual, we consistently refer to "archives" and "archive members" to
544 make learning to use `tar' easier for novice users.
547 File: tar.info, Node: Authors, Next: Reports, Prev: Naming tar Archives, Up: Introduction
549 1.5 GNU `tar' Authors
550 =====================
552 GNU `tar' was originally written by John Gilmore, and modified by many
553 people. The GNU enhancements were written by Jay Fenlason, then Joy
554 Kendall, and the whole package has been further maintained by Thomas
555 Bushnell, n/BSG, Franc,ois Pinard, Paul Eggert, and finally Sergey
556 Poznyakoff with the help of numerous and kind users.
558 We wish to stress that `tar' is a collective work, and owes much to
559 all those people who reported problems, offered solutions and other
560 insights, or shared their thoughts and suggestions. An impressive, yet
561 partial list of those contributors can be found in the `THANKS' file
562 from the GNU `tar' distribution.
564 Jay Fenlason put together a draft of a GNU `tar' manual, borrowing
565 notes from the original man page from John Gilmore. This was withdrawn
566 in version 1.11. Thomas Bushnell, n/BSG and Amy Gorin worked on a
567 tutorial and manual for GNU `tar'. Franc,ois Pinard put version 1.11.8
568 of the manual together by taking information from all these sources and
569 merging them. Melissa Weisshaus finally edited and redesigned the book
570 to create version 1.12. The book for versions from 1.14 up to 1.24
571 were edited by the current maintainer, Sergey Poznyakoff.
573 For version 1.12, Daniel Hagerty contributed a great deal of
574 technical consulting. In particular, he is the primary author of *note
577 In July, 2003 GNU `tar' was put on CVS at savannah.gnu.org (see
578 `http://savannah.gnu.org/projects/tar'), and active development and
579 maintenance work has started again. Currently GNU `tar' is being
580 maintained by Paul Eggert, Sergey Poznyakoff and Jeff Bailey.
582 Support for POSIX archives was added by Sergey Poznyakoff.
585 File: tar.info, Node: Reports, Prev: Authors, Up: Introduction
587 1.6 Reporting bugs or suggestions
588 =================================
590 If you find problems or have suggestions about this program or manual,
591 please report them to `bug-tar@gnu.org'.
593 When reporting a bug, please be sure to include as much detail as
594 possible, in order to reproduce it.
597 File: tar.info, Node: Tutorial, Next: tar invocation, Prev: Introduction, Up: Top
599 2 Tutorial Introduction to `tar'
600 ********************************
602 This chapter guides you through some basic examples of three `tar'
603 operations: `--create', `--list', and `--extract'. If you already know
604 how to use some other version of `tar', then you may not need to read
605 this chapter. This chapter omits most complicated details about how
611 * stylistic conventions::
612 * basic tar options:: Basic `tar' Operations and Options
613 * frequent operations::
614 * Two Frequent Options::
615 * create:: How to Create Archives
616 * list:: How to List Archives
617 * extract:: How to Extract Members from an Archive
621 File: tar.info, Node: assumptions, Next: stylistic conventions, Up: Tutorial
623 2.1 Assumptions this Tutorial Makes
624 ===================================
626 This chapter is paced to allow beginners to learn about `tar' slowly.
627 At the same time, we will try to cover all the basic aspects of these
628 three operations. In order to accomplish both of these tasks, we have
629 made certain assumptions about your knowledge before reading this
630 manual, and the hardware you will be using:
632 * Before you start to work through this tutorial, you should
633 understand what the terms "archive" and "archive member" mean
634 (*note Definitions::). In addition, you should understand
635 something about how Unix-type operating systems work, and you
636 should know how to use some basic utilities. For example, you
637 should know how to create, list, copy, rename, edit, and delete
638 files and directories; how to change between directories; and how
639 to figure out where you are in the file system. You should have
640 some basic understanding of directory structure and how files are
641 named according to which directory they are in. You should
642 understand concepts such as standard output and standard input,
643 what various definitions of the term `argument' mean, and the
644 differences between relative and absolute file names.
646 * This manual assumes that you are working from your own home
647 directory (unless we state otherwise). In this tutorial, you will
648 create a directory to practice `tar' commands in. When we show
649 file names, we will assume that those names are relative to your
650 home directory. For example, my home directory is
651 `/home/fsf/melissa'. All of my examples are in a subdirectory of
652 the directory named by that file name; the subdirectory is called
655 * In general, we show examples of archives which exist on (or can be
656 written to, or worked with from) a directory on a hard disk. In
657 most cases, you could write those archives to, or work with them
658 on any other device, such as a tape drive. However, some of the
659 later examples in the tutorial and next chapter will not work on
660 tape drives. Additionally, working with tapes is much more
661 complicated than working with hard disks. For these reasons, the
662 tutorial does not cover working with tape drives. *Note Media::,
663 for complete information on using `tar' archives with tape drives.
667 File: tar.info, Node: stylistic conventions, Next: basic tar options, Prev: assumptions, Up: Tutorial
669 2.2 Stylistic Conventions
670 =========================
672 In the examples, `$' represents a typical shell prompt. It precedes
673 lines you should type; to make this more clear, those lines are shown
674 in `this font', as opposed to lines which represent the computer's
675 response; those lines are shown in `this font', or sometimes `like
679 File: tar.info, Node: basic tar options, Next: frequent operations, Prev: stylistic conventions, Up: Tutorial
681 2.3 Basic `tar' Operations and Options
682 ======================================
684 `tar' can take a wide variety of arguments which specify and define the
685 actions it will have on the particular set of files or the archive.
686 The main types of arguments to `tar' fall into one of two classes:
687 operations, and options.
689 Some arguments fall into a class called "operations"; exactly one of
690 these is both allowed and required for any instance of using `tar'; you
691 may _not_ specify more than one. People sometimes speak of "operating
692 modes". You are in a particular operating mode when you have specified
693 the operation which specifies it; there are eight operations in total,
694 and thus there are eight operating modes.
696 The other arguments fall into the class known as "options". You are
697 not required to specify any options, and you are allowed to specify more
698 than one at a time (depending on the way you are using `tar' at that
699 time). Some options are used so frequently, and are so useful for
700 helping you type commands more carefully that they are effectively
701 "required". We will discuss them in this chapter.
703 You can write most of the `tar' operations and options in any of
704 three forms: long (mnemonic) form, short form, and old style. Some of
705 the operations and options have no short or "old" forms; however, the
706 operations and options which we will cover in this tutorial have
707 corresponding abbreviations. We will indicate those abbreviations
708 appropriately to get you used to seeing them. Note, that the "old
709 style" option forms exist in GNU `tar' for compatibility with Unix
710 `tar'. In this book we present a full discussion of this way of
711 writing options and operations (*note Old Options::), and we discuss
712 the other two styles of writing options (*Note Long Options::, and
713 *note Short Options::).
715 In the examples and in the text of this tutorial, we usually use the
716 long forms of operations and options; but the "short" forms produce the
717 same result and can make typing long `tar' commands easier. For
718 example, instead of typing
720 tar --create --verbose --file=afiles.tar apple angst aspic
723 tar -c -v -f afiles.tar apple angst aspic
726 tar -cvf afiles.tar apple angst aspic
728 For more information on option syntax, see *note Advanced tar::. In
729 discussions in the text, when we name an option by its long form, we
730 also give the corresponding short option in parentheses.
732 The term, "option", can be confusing at times, since "operations"
733 are often lumped in with the actual, _optional_ "options" in certain
734 general class statements. For example, we just talked about "short and
735 long forms of options and operations". However, experienced `tar'
736 users often refer to these by shorthand terms such as, "short and long
737 options". This term assumes that the "operations" are included, also.
738 Context will help you determine which definition of "options" to use.
740 Similarly, the term "command" can be confusing, as it is often used
741 in two different ways. People sometimes refer to `tar' "commands". A
742 `tar' "command" is the entire command line of user input which tells
743 `tar' what to do -- including the operation, options, and any arguments
744 (file names, pipes, other commands, etc.). However, you will also
745 sometimes hear the term "the `tar' command". When the word "command"
746 is used specifically like this, a person is usually referring to the
747 `tar' _operation_, not the whole line. Again, use context to figure
748 out which of the meanings the speaker intends.
751 File: tar.info, Node: frequent operations, Next: Two Frequent Options, Prev: basic tar options, Up: Tutorial
753 2.4 The Three Most Frequently Used Operations
754 =============================================
756 Here are the three most frequently used operations (both short and long
757 forms), as well as a brief description of their meanings. The rest of
758 this chapter will cover how to use these operations in detail. We will
759 present the rest of the operations in the next chapter.
763 Create a new `tar' archive.
767 List the contents of an archive.
771 Extract one or more members from an archive.
774 File: tar.info, Node: Two Frequent Options, Next: create, Prev: frequent operations, Up: Tutorial
776 2.5 Two Frequently Used Options
777 ===============================
779 To understand how to run `tar' in the three operating modes listed
780 previously, you also need to understand how to use two of the options to
781 `tar': `--file' (which takes an archive file as an argument) and
782 `--verbose'. (You are usually not _required_ to specify either of
783 these options when you run `tar', but they can be very useful in making
784 things more clear and helping you avoid errors.)
793 File: tar.info, Node: file tutorial, Next: verbose tutorial, Up: Two Frequent Options
798 `--file=ARCHIVE-NAME'
800 Specify the name of an archive file.
802 You can specify an argument for the `--file=ARCHIVE-NAME' (`-f
803 ARCHIVE-NAME') option whenever you use `tar'; this option determines
804 the name of the archive file that `tar' will work on.
806 If you don't specify this argument, then `tar' will examine the
807 environment variable `TAPE'. If it is set, its value will be used as
808 the archive name. Otherwise, `tar' will use the default archive,
809 determined at compile time. Usually it is standard output or some
810 physical tape drive attached to your machine (you can verify what the
811 default is by running `tar --show-defaults', *note defaults::). If
812 there is no tape drive attached, or the default is not meaningful, then
813 `tar' will print an error message. The error message might look
814 roughly like one of the following:
816 tar: can't open /dev/rmt8 : No such device or address
817 tar: can't open /dev/rsmt0 : I/O error
819 To avoid confusion, we recommend that you always specify an archive file
820 name by using `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') when writing
821 your `tar' commands. For more information on using the
822 `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option, see *note file::.
825 File: tar.info, Node: verbose tutorial, Next: help tutorial, Prev: file tutorial, Up: Two Frequent Options
827 The `--verbose' Option
828 ----------------------
832 Show the files being worked on as `tar' is running.
834 `--verbose' (`-v') shows details about the results of running `tar'.
835 This can be especially useful when the results might not be obvious.
836 For example, if you want to see the progress of `tar' as it writes
837 files into the archive, you can use the `--verbose' option. In the
838 beginning, you may find it useful to use `--verbose' at all times; when
839 you are more accustomed to `tar', you will likely want to use it at
840 certain times but not at others. We will use `--verbose' at times to
841 help make something clear, and we will give many examples both using
842 and not using `--verbose' to show the differences.
844 Each instance of `--verbose' on the command line increases the
845 verbosity level by one, so if you need more details on the output,
848 When reading archives (`--list', `--extract', `--diff'), `tar' by
849 default prints only the names of the members being extracted. Using
850 `--verbose' will show a full, `ls' style member listing.
852 In contrast, when writing archives (`--create', `--append',
853 `--update'), `tar' does not print file names by default. So, a single
854 `--verbose' option shows the file names being added to the archive,
855 while two `--verbose' options enable the full listing.
857 For example, to create an archive in verbose mode:
859 $ tar -cvf afiles.tar apple angst aspic
864 Creating the same archive with the verbosity level 2 could give:
866 $ tar -cvvf afiles.tar apple angst aspic
867 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
868 -rw-r--r-- gray/staff 11481 2006-06-09 12:06 angst
869 -rw-r--r-- gray/staff 23152 2006-06-09 12:06 aspic
871 This works equally well using short or long forms of options. Using
872 long forms, you would simply write out the mnemonic form of the option
875 $ tar --create --verbose --verbose ...
877 Note that you must double the hyphens properly each time.
879 Later in the tutorial, we will give examples using
880 `--verbose --verbose'.
882 The full output consists of six fields:
884 * File type and permissions in symbolic form. These are displayed
885 in the same format as the first column of `ls -l' output (*note
886 format=verbose: (fileutils)What information is listed.).
888 * Owner name and group separated by a slash character. If these
889 data are not available (for example, when listing a `v7' format
890 archive), numeric ID values are printed instead.
892 * Size of the file, in bytes.
894 * File modification date in ISO 8601 format.
896 * File modification time.
898 * File name. If the name contains any special characters (white
899 space, newlines, etc.) these are displayed in an unambiguous form
900 using so called "quoting style". For the detailed discussion of
901 available styles and on how to use them, see *note quoting
904 Depending on the file type, the name can be followed by some
905 additional information, described in the following table:
908 The file or archive member is a "symbolic link" and LINK-NAME
909 is the name of file it links to.
912 The file or archive member is a "hard link" and LINK-NAME is
913 the name of file it links to.
916 The archive member is an old GNU format long link. You will
917 normally not encounter this.
920 The archive member is an old GNU format long name. You will
921 normally not encounter this.
924 The archive member is a GNU "volume header" (*note Tape
927 `--Continued at byte N--'
928 Encountered only at the beginning of a multi-volume archive
929 (*note Using Multiple Tapes::). This archive member is a
930 continuation from the previous volume. The number N gives the
931 offset where the original file was split.
933 `unknown file type C'
934 An archive member of unknown type. C is the type character
935 from the archive header. If you encounter such a message, it
936 means that either your archive contains proprietary member
937 types GNU `tar' is not able to handle, or the archive is
941 For example, here is an archive listing containing most of the
942 special suffixes explained above:
944 V--------- 0/0 1536 2006-06-09 13:07 MyVolume--Volume Header--
945 -rw-r--r-- gray/staff 456783 2006-06-09 12:06 aspic--Continued at
947 -rw-r--r-- gray/staff 62373 2006-06-09 12:06 apple
948 lrwxrwxrwx gray/staff 0 2006-06-09 13:01 angst -> apple
949 -rw-r--r-- gray/staff 35793 2006-06-09 12:06 blues
950 hrw-r--r-- gray/staff 0 2006-06-09 12:06 music link to blues
954 File: tar.info, Node: help tutorial, Prev: verbose tutorial, Up: Two Frequent Options
956 Getting Help: Using the `--help' Option
957 ---------------------------------------
960 The `--help' option to `tar' prints out a very brief list of all
961 operations and option available for the current version of `tar'
962 available on your system.
965 File: tar.info, Node: create, Next: list, Prev: Two Frequent Options, Up: Tutorial
967 2.6 How to Create Archives
968 ==========================
970 _(This message will disappear, once this node revised.)_
972 One of the basic operations of `tar' is `--create' (`-c'), which you
973 use to create a `tar' archive. We will explain `--create' first
974 because, in order to learn about the other operations, you will find it
975 useful to have an archive available to practice on.
977 To make this easier, in this section you will first create a
978 directory containing three files. Then, we will show you how to create
979 an _archive_ (inside the new directory). Both the directory, and the
980 archive are specifically for you to practice on. The rest of this
981 chapter and the next chapter will show many examples using this
982 directory and the files you will create: some of those files may be
983 other directories and other archives.
985 The three files you will archive in this example are called `blues',
986 `folk', and `jazz'. The archive is called `collection.tar'.
988 This section will proceed slowly, detailing how to use `--create' in
989 `verbose' mode, and showing examples using both short and long forms.
990 In the rest of the tutorial, and in the examples in the next chapter,
991 we will proceed at a slightly quicker pace. This section moves more
992 slowly to allow beginning users to understand how `tar' works.
996 * prepare for examples::
997 * Creating the archive::
1003 File: tar.info, Node: prepare for examples, Next: Creating the archive, Up: create
1005 2.6.1 Preparing a Practice Directory for Examples
1006 -------------------------------------------------
1008 To follow along with this and future examples, create a new directory
1009 called `practice' containing files called `blues', `folk' and `jazz'.
1010 The files can contain any information you like: ideally, they should
1011 contain information which relates to their names, and be of different
1012 lengths. Our examples assume that `practice' is a subdirectory of your
1015 Now `cd' to the directory named `practice'; `practice' is now your
1016 "working directory". (_Please note_: Although the full file name of
1017 this directory is `/HOMEDIR/practice', in our examples we will refer to
1018 this directory as `practice'; the HOMEDIR is presumed.)
1020 In general, you should check that the files to be archived exist
1021 where you think they do (in the working directory) by running `ls'.
1022 Because you just created the directory and the files and have changed to
1023 that directory, you probably don't need to do that this time.
1025 It is very important to make sure there isn't already a file in the
1026 working directory with the archive name you intend to use (in this case,
1027 `collection.tar'), or that you don't care about its contents. Whenever
1028 you use `create', `tar' will erase the current contents of the file
1029 named by `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') if it exists. `tar'
1030 will not tell you if you are about to overwrite an archive unless you
1031 specify an option which does this (*note backup::, for the information
1032 on how to do so). To add files to an existing archive, you need to use
1033 a different option, such as `--append' (`-r'); see *note append:: for
1034 information on how to do this.
1037 File: tar.info, Node: Creating the archive, Next: create verbose, Prev: prepare for examples, Up: create
1039 2.6.2 Creating the Archive
1040 --------------------------
1042 To place the files `blues', `folk', and `jazz' into an archive named
1043 `collection.tar', use the following command:
1045 $ tar --create --file=collection.tar blues folk jazz
1047 The order of the arguments is not very important, _when using long
1048 option forms_. You could also say:
1050 $ tar blues --create folk --file=collection.tar jazz
1052 However, you can see that this order is harder to understand; this is
1053 why we will list the arguments in the order that makes the commands
1054 easiest to understand (and we encourage you to do the same when you use
1055 `tar', to avoid errors).
1057 Note that the sequence `--file=collection.tar' is considered to be
1058 _one_ argument. If you substituted any other string of characters for
1059 `collection.tar', then that string would become the name of the
1060 archive file you create.
1062 The order of the options becomes more important when you begin to use
1063 short forms. With short forms, if you type commands in the wrong order
1064 (even if you type them correctly in all other ways), you may end up with
1065 results you don't expect. For this reason, it is a good idea to get
1066 into the habit of typing options in the order that makes inherent sense.
1067 *Note short create::, for more information on this.
1069 In this example, you type the command as shown above: `--create' is
1070 the operation which creates the new archive (`collection.tar'), and
1071 `--file' is the option which lets you give it the name you chose. The
1072 files, `blues', `folk', and `jazz', are now members of the archive,
1073 `collection.tar' (they are "file name arguments" to the `--create'
1074 operation. *Note Choosing::, for the detailed discussion on these.)
1075 Now that they are in the archive, they are called _archive members_,
1076 not files. (*note members: Definitions.).
1078 When you create an archive, you _must_ specify which files you want
1079 placed in the archive. If you do not specify any archive members, GNU
1080 `tar' will complain.
1082 If you now list the contents of the working directory (`ls'), you
1083 will find the archive file listed as well as the files you saw
1086 blues folk jazz collection.tar
1088 Creating the archive `collection.tar' did not destroy the copies of the
1089 files in the directory.
1091 Keep in mind that if you don't indicate an operation, `tar' will not
1092 run and will prompt you for one. If you don't name any files, `tar'
1093 will complain. You must have write access to the working directory, or
1094 else you will not be able to create an archive in that directory.
1096 _Caution_: Do not attempt to use `--create' (`-c') to add files to
1097 an existing archive; it will delete the archive and write a new one.
1098 Use `--append' (`-r') instead. *Note append::.
1101 File: tar.info, Node: create verbose, Next: short create, Prev: Creating the archive, Up: create
1103 2.6.3 Running `--create' with `--verbose'
1104 -----------------------------------------
1106 If you include the `--verbose' (`-v') option on the command line, `tar'
1107 will list the files it is acting on as it is working. In verbose mode,
1108 the `create' example above would appear as:
1110 $ tar --create --verbose --file=collection.tar blues folk jazz
1115 This example is just like the example we showed which did not use
1116 `--verbose', except that `tar' generated the remaining lines.
1118 In the rest of the examples in this chapter, we will frequently use
1119 `verbose' mode so we can show actions or `tar' responses that you would
1120 otherwise not see, and which are important for you to understand.
1123 File: tar.info, Node: short create, Next: create dir, Prev: create verbose, Up: create
1125 2.6.4 Short Forms with `create'
1126 -------------------------------
1128 As we said before, the `--create' (`-c') operation is one of the most
1129 basic uses of `tar', and you will use it countless times. Eventually,
1130 you will probably want to use abbreviated (or "short") forms of
1131 options. A full discussion of the three different forms that options
1132 can take appears in *note Styles::; for now, here is what the previous
1133 example (including the `--verbose' (`-v') option) looks like using
1136 $ tar -cvf collection.tar blues folk jazz
1141 As you can see, the system responds the same no matter whether you use
1142 long or short option forms.
1144 One difference between using short and long option forms is that,
1145 although the exact placement of arguments following options is no more
1146 specific when using short forms, it is easier to become confused and
1147 make a mistake when using short forms. For example, suppose you
1148 attempted the above example in the following way:
1150 $ tar -cfv collection.tar blues folk jazz
1152 In this case, `tar' will make an archive file called `v', containing
1153 the files `blues', `folk', and `jazz', because the `v' is the closest
1154 "file name" to the `-f' option, and is thus taken to be the chosen
1155 archive file name. `tar' will try to add a file called
1156 `collection.tar' to the `v' archive file; if the file `collection.tar'
1157 did not already exist, `tar' will report an error indicating that this
1158 file does not exist. If the file `collection.tar' does already exist
1159 (e.g., from a previous command you may have run), then `tar' will add
1160 this file to the archive. Because the `-v' option did not get
1161 registered, `tar' will not run under `verbose' mode, and will not
1162 report its progress.
1164 The end result is that you may be quite confused about what happened,
1165 and possibly overwrite a file. To illustrate this further, we will show
1166 you how an example we showed previously would look using short forms.
1170 $ tar blues --create folk --file=collection.tar jazz
1172 is confusing as it is. When shown using short forms, however, it
1173 becomes much more so:
1175 $ tar blues -c folk -f collection.tar jazz
1177 It would be very easy to put the wrong string of characters immediately
1178 following the `-f', but doing that could sacrifice valuable data.
1180 For this reason, we recommend that you pay very careful attention to
1181 the order of options and placement of file and archive names,
1182 especially when using short option forms. Not having the option name
1183 written out mnemonically can affect how well you remember which option
1184 does what, and therefore where different names have to be placed.
1187 File: tar.info, Node: create dir, Prev: short create, Up: create
1189 2.6.5 Archiving Directories
1190 ---------------------------
1192 You can archive a directory by specifying its directory name as a file
1193 name argument to `tar'. The files in the directory will be archived
1194 relative to the working directory, and the directory will be re-created
1195 along with its contents when the archive is extracted.
1197 To archive a directory, first move to its superior directory. If you
1198 have followed the previous instructions in this tutorial, you should
1204 This will put you into the directory which contains `practice', i.e.,
1205 your home directory. Once in the superior directory, you can specify
1206 the subdirectory, `practice', as a file name argument. To store
1207 `practice' in the new archive file `music.tar', type:
1209 $ tar --create --verbose --file=music.tar practice
1211 `tar' should output:
1217 practice/collection.tar
1219 Note that the archive thus created is not in the subdirectory
1220 `practice', but rather in the current working directory--the directory
1221 from which `tar' was invoked. Before trying to archive a directory
1222 from its superior directory, you should make sure you have write access
1223 to the superior directory itself, not only the directory you are trying
1224 archive with `tar'. For example, you will probably not be able to
1225 store your home directory in an archive by invoking `tar' from the root
1226 directory; *Note absolute::. (Note also that `collection.tar', the
1227 original archive file, has itself been archived. `tar' will accept any
1228 file as a file to be archived, regardless of its content. When
1229 `music.tar' is extracted, the archive file `collection.tar' will be
1230 re-written into the file system).
1232 If you give `tar' a command such as
1234 $ tar --create --file=foo.tar .
1236 `tar' will report `tar: ./foo.tar is the archive; not dumped'. This
1237 happens because `tar' creates the archive `foo.tar' in the current
1238 directory before putting any files into it. Then, when `tar' attempts
1239 to add all the files in the directory `.' to the archive, it notices
1240 that the file `./foo.tar' is the same as the archive `foo.tar', and
1241 skips it. (It makes no sense to put an archive into itself.) GNU `tar'
1242 will continue in this case, and create the archive normally, except for
1243 the exclusion of that one file. (_Please note:_ Other implementations
1244 of `tar' may not be so clever; they will enter an infinite loop when
1245 this happens, so you should not depend on this behavior unless you are
1246 certain you are running GNU `tar'. In general, it is wise to always
1247 place the archive outside of the directory being dumped.)
1250 File: tar.info, Node: list, Next: extract, Prev: create, Up: Tutorial
1252 2.7 How to List Archives
1253 ========================
1255 Frequently, you will find yourself wanting to determine exactly what a
1256 particular archive contains. You can use the `--list' (`-t') operation
1257 to get the member names as they currently appear in the archive, as
1258 well as various attributes of the files at the time they were archived.
1259 For example, you can examine the archive `collection.tar' that you
1260 created in the last section with the command,
1262 $ tar --list --file=collection.tar
1264 The output of `tar' would then be:
1270 The archive `bfiles.tar' would list as follows:
1276 Be sure to use a `--file=ARCHIVE-NAME' (`-f ARCHIVE-NAME') option just
1277 as with `--create' (`-c') to specify the name of the archive.
1279 If you use the `--verbose' (`-v') option with `--list', then `tar'
1280 will print out a listing reminiscent of `ls -l', showing owner, file
1281 size, and so forth. This output is described in detail in *note
1282 verbose member listing::.
1284 If you had used `--verbose' (`-v') mode, the example above would
1287 $ tar --list --verbose --file=collection.tar folk
1288 -rw-r--r-- myself user 62 1990-05-23 10:55 folk
1290 It is important to notice that the output of `tar --list --verbose'
1291 does not necessarily match that produced by `tar --create --verbose'
1292 while creating the archive. It is because GNU `tar', unless told
1293 explicitly not to do so, removes some directory prefixes from file
1294 names before storing them in the archive (*Note absolute::, for more
1295 information). In other words, in verbose mode GNU `tar' shows "file
1296 names" when creating an archive and "member names" when listing it.
1297 Consider this example:
1299 $ tar --create --verbose --file archive /etc/mail
1300 tar: Removing leading `/' from member names
1302 /etc/mail/sendmail.cf
1304 $ tar --test --file archive
1306 etc/mail/sendmail.cf
1309 This default behavior can sometimes be inconvenient. You can force
1310 GNU `tar' show member names when creating archive by supplying
1311 `--show-stored-names' option.
1313 `--show-stored-names'
1314 Print member (as opposed to _file_) names when creating the
1317 You can specify one or more individual member names as arguments when
1318 using `list'. In this case, `tar' will only list the names of members
1319 you identify. For example, `tar --list --file=afiles.tar apple' would
1322 Because `tar' preserves file names, these must be specified as they
1323 appear in the archive (i.e., relative to the directory from which the
1324 archive was created). Therefore, it is essential when specifying
1325 member names to `tar' that you give the exact member names. For
1326 example, `tar --list --file=bfiles.tar birds' would produce an error
1327 message something like `tar: birds: Not found in archive', because
1328 there is no member named `birds', only one named `./birds'. While the
1329 names `birds' and `./birds' name the same file, _member_ names by
1330 default are compared verbatim.
1332 However, `tar --list --file=bfiles.tar baboon' would respond with
1333 `baboon', because this exact member name is in the archive file
1334 `bfiles.tar'. If you are not sure of the exact file name, use
1335 "globbing patterns", for example:
1337 $ tar --list --file=bfiles.tar --wildcards '*b*'
1339 will list all members whose name contains `b'. *Note wildcards::, for
1340 a detailed discussion of globbing patterns and related `tar' command
1348 File: tar.info, Node: list dir, Up: list
1350 Listing the Contents of a Stored Directory
1351 ------------------------------------------
1353 To get information about the contents of an archived directory, use the
1354 directory name as a file name argument in conjunction with `--list'
1355 (`-t'). To find out file attributes, include the `--verbose' (`-v')
1358 For example, to find out about files in the directory `practice', in
1359 the archive file `music.tar', type:
1361 $ tar --list --verbose --file=music.tar practice
1365 drwxrwxrwx myself user 0 1990-05-31 21:49 practice/
1366 -rw-r--r-- myself user 42 1990-05-21 13:29 practice/blues
1367 -rw-r--r-- myself user 62 1990-05-23 10:55 practice/folk
1368 -rw-r--r-- myself user 40 1990-05-21 13:30 practice/jazz
1369 -rw-r--r-- myself user 10240 1990-05-31 21:49 practice/collection.tar
1371 When you use a directory name as a file name argument, `tar' acts on
1372 all the files (including sub-directories) in that directory.
1375 File: tar.info, Node: extract, Next: going further, Prev: list, Up: Tutorial
1377 2.8 How to Extract Members from an Archive
1378 ==========================================
1380 Creating an archive is only half the job--there is no point in storing
1381 files in an archive if you can't retrieve them. The act of retrieving
1382 members from an archive so they can be used and manipulated as
1383 unarchived files again is called "extraction". To extract files from
1384 an archive, use the `--extract' (`--get' or `-x') operation. As with
1385 `--create', specify the name of the archive with `--file' (`-f')
1386 option. Extracting an archive does not modify the archive in any way;
1387 you can extract it multiple times if you want or need to.
1389 Using `--extract', you can extract an entire archive, or specific
1390 files. The files can be directories containing other files, or not. As
1391 with `--create' (`-c') and `--list' (`-t'), you may use the short or the
1392 long form of the operation without affecting the performance.
1396 * extracting archives::
1397 * extracting files::
1399 * extracting untrusted archives::
1400 * failing commands::
1403 File: tar.info, Node: extracting archives, Next: extracting files, Up: extract
1405 2.8.1 Extracting an Entire Archive
1406 ----------------------------------
1408 To extract an entire archive, specify the archive file name only, with
1409 no individual file names as arguments. For example,
1411 $ tar -xvf collection.tar
1415 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
1416 -rw-r--r-- me user 21 1996-09-23 16:44 blues
1417 -rw-r--r-- me user 20 1996-09-23 16:44 folk
1420 File: tar.info, Node: extracting files, Next: extract dir, Prev: extracting archives, Up: extract
1422 2.8.2 Extracting Specific Files
1423 -------------------------------
1425 To extract specific archive members, give their exact member names as
1426 arguments, as printed by `--list' (`-t'). If you had mistakenly
1427 deleted one of the files you had placed in the archive `collection.tar'
1428 earlier (say, `blues'), you can extract it from the archive without
1429 changing the archive's structure. Its contents will be identical to
1430 the original file `blues' that you deleted.
1432 First, make sure you are in the `practice' directory, and list the
1433 files in the directory. Now, delete the file, `blues', and list the
1434 files in the directory again.
1436 You can now extract the member `blues' from the archive file
1437 `collection.tar' like this:
1439 $ tar --extract --file=collection.tar blues
1441 If you list the files in the directory again, you will see that the file
1442 `blues' has been restored, with its original permissions, data
1443 modification times, and owner.(1) (These parameters will be identical
1444 to those which the file had when you originally placed it in the
1445 archive; any changes you may have made before deleting the file from
1446 the file system, however, will _not_ have been made to the archive
1447 member.) The archive file, `collection.tar', is the same as it was
1448 before you extracted `blues'. You can confirm this by running `tar'
1449 with `--list' (`-t').
1451 Remember that as with other operations, specifying the exact member
1452 name is important. `tar --extract --file=bfiles.tar birds' will fail,
1453 because there is no member named `birds'. To extract the member named
1454 `./birds', you must specify `tar --extract --file=bfiles.tar ./birds'.
1455 If you don't remember the exact member names, use `--list' (`-t') option
1456 (*note list::). You can also extract those members that match a
1457 specific "globbing pattern". For example, to extract from `bfiles.tar'
1458 all files that begin with `b', no matter their directory prefix, you
1461 $ tar -x -f bfiles.tar --wildcards --no-anchored 'b*'
1463 Here, `--wildcards' instructs `tar' to treat command line arguments as
1464 globbing patterns and `--no-anchored' informs it that the patterns
1465 apply to member names after any `/' delimiter. The use of globbing
1466 patterns is discussed in detail in *Note wildcards::.
1468 You can extract a file to standard output by combining the above
1469 options with the `--to-stdout' (`-O') option (*note Writing to Standard
1472 If you give the `--verbose' option, then `--extract' will print the
1473 names of the archive members as it extracts them.
1475 ---------- Footnotes ----------
1477 (1) This is only accidentally true, but not in general. Whereas
1478 modification times are always restored, in most cases, one has to be
1479 root for restoring the owner, and use a special option for restoring
1480 permissions. Here, it just happens that the restoring user is also the
1481 owner of the archived members, and that the current `umask' is
1482 compatible with original permissions.
1485 File: tar.info, Node: extract dir, Next: extracting untrusted archives, Prev: extracting files, Up: extract
1487 2.8.3 Extracting Files that are Directories
1488 -------------------------------------------
1490 Extracting directories which are members of an archive is similar to
1491 extracting other files. The main difference to be aware of is that if
1492 the extracted directory has the same name as any directory already in
1493 the working directory, then files in the extracted directory will be
1494 placed into the directory of the same name. Likewise, if there are
1495 files in the pre-existing directory with the same names as the members
1496 which you extract, the files from the extracted archive will replace
1497 the files already in the working directory (and possible
1498 subdirectories). This will happen regardless of whether or not the
1499 files in the working directory were more recent than those extracted
1500 (there exist, however, special options that alter this behavior *note
1503 However, if a file was stored with a directory name as part of its
1504 file name, and that directory does not exist under the working
1505 directory when the file is extracted, `tar' will create the directory.
1507 We can demonstrate how to use `--extract' to extract a directory
1508 file with an example. Change to the `practice' directory if you
1509 weren't there, and remove the files `folk' and `jazz'. Then, go back
1510 to the parent directory and extract the archive `music.tar'. You may
1511 either extract the entire archive, or you may extract only the files
1512 you just deleted. To extract the entire archive, don't give any file
1513 names as arguments after the archive name `music.tar'. To extract only
1514 the files you deleted, use the following command:
1516 $ tar -xvf music.tar practice/folk practice/jazz
1520 If you were to specify two `--verbose' (`-v') options, `tar' would have
1521 displayed more detail about the extracted files, as shown in the
1524 $ tar -xvvf music.tar practice/folk practice/jazz
1525 -rw-r--r-- me user 28 1996-10-18 16:31 practice/jazz
1526 -rw-r--r-- me user 20 1996-09-23 16:44 practice/folk
1528 Because you created the directory with `practice' as part of the file
1529 names of each of the files by archiving the `practice' directory as
1530 `practice', you must give `practice' as part of the file names when you
1531 extract those files from the archive.
1534 File: tar.info, Node: extracting untrusted archives, Next: failing commands, Prev: extract dir, Up: extract
1536 2.8.4 Extracting Archives from Untrusted Sources
1537 ------------------------------------------------
1539 Extracting files from archives can overwrite files that already exist.
1540 If you receive an archive from an untrusted source, you should make a
1541 new directory and extract into that directory, so that you don't have
1542 to worry about the extraction overwriting one of your existing files.
1543 For example, if `untrusted.tar' came from somewhere else on the
1544 Internet, and you don't necessarily trust its contents, you can extract
1549 $ tar -xvf ../untrusted.tar
1551 It is also a good practice to examine contents of the archive before
1552 extracting it, using `--list' (`-t') option, possibly combined with
1556 File: tar.info, Node: failing commands, Prev: extracting untrusted archives, Up: extract
1558 2.8.5 Commands That Will Fail
1559 -----------------------------
1561 Here are some sample commands you might try which will not work, and why
1564 If you try to use this command,
1566 $ tar -xvf music.tar folk jazz
1568 you will get the following response:
1570 tar: folk: Not found in archive
1571 tar: jazz: Not found in archive
1573 This is because these files were not originally _in_ the parent
1574 directory `..', where the archive is located; they were in the
1575 `practice' directory, and their file names reflect this:
1577 $ tar -tvf music.tar
1582 Likewise, if you try to use this command,
1584 $ tar -tvf music.tar folk jazz
1586 you would get a similar response. Members with those names are not in
1587 the archive. You must use the correct member names, or wildcards, in
1588 order to extract the files from the archive.
1590 If you have forgotten the correct names of the files in the archive,
1591 use `tar --list --verbose' to list them correctly.
1594 File: tar.info, Node: going further, Prev: extract, Up: Tutorial
1596 2.9 Going Further Ahead in this Manual
1597 ======================================
1599 _(This message will disappear, once this node revised.)_
1602 File: tar.info, Node: tar invocation, Next: operations, Prev: Tutorial, Up: Top
1604 3 Invoking GNU `tar'
1605 ********************
1607 This chapter is about how one invokes the GNU `tar' command, from the
1608 command synopsis (*note Synopsis::). There are numerous options, and
1609 many styles for writing them. One mandatory option specifies the
1610 operation `tar' should perform (*note Operation Summary::), other
1611 options are meant to detail how this operation should be performed
1612 (*note Option Summary::). Non-option arguments are not always
1613 interpreted the same way, depending on what the operation is.
1615 You will find in this chapter everything about option styles and
1616 rules for writing them (*note Styles::). On the other hand, operations
1617 and options are fully described elsewhere, in other chapters. Here,
1618 you will find only synthetic descriptions for operations and options,
1619 together with pointers to other parts of the `tar' manual.
1621 Some options are so special they are fully described right in this
1622 chapter. They have the effect of inhibiting the normal operation of
1623 `tar' or else, they globally alter the amount of feedback the user
1624 receives about what is going on. These are the `--help' and
1625 `--version' (*note help::), `--verbose' (*note verbose::) and
1626 `--interactive' options (*note interactive::).
1631 * using tar options::
1642 File: tar.info, Node: Synopsis, Next: using tar options, Up: tar invocation
1644 3.1 General Synopsis of `tar'
1645 =============================
1647 The GNU `tar' program is invoked as either one of:
1649 tar OPTION... [NAME]...
1650 tar LETTER... [ARGUMENT]... [OPTION]... [NAME]...
1652 The second form is for when old options are being used.
1654 You can use `tar' to store files in an archive, to extract them from
1655 an archive, and to do other types of archive manipulation. The primary
1656 argument to `tar', which is called the "operation", specifies which
1657 action to take. The other arguments to `tar' are either "options",
1658 which change the way `tar' performs an operation, or file names or
1659 archive members, which specify the files or members `tar' is to act on.
1661 You can actually type in arguments in any order, even if in this
1662 manual the options always precede the other arguments, to make examples
1663 easier to understand. Further, the option stating the main operation
1664 mode (the `tar' main command) is usually given first.
1666 Each NAME in the synopsis above is interpreted as an archive member
1667 name when the main command is one of `--compare' (`--diff', `-d'),
1668 `--delete', `--extract' (`--get', `-x'), `--list' (`-t') or `--update'
1669 (`-u'). When naming archive members, you must give the exact name of
1670 the member in the archive, as it is printed by `--list'. For
1671 `--append' (`-r') and `--create' (`-c'), these NAME arguments specify
1672 the names of either files or directory hierarchies to place in the
1673 archive. These files or hierarchies should already exist in the file
1674 system, prior to the execution of the `tar' command.
1676 `tar' interprets relative file names as being relative to the
1677 working directory. `tar' will make all file names relative (by
1678 removing leading slashes when archiving or restoring files), unless you
1679 specify otherwise (using the `--absolute-names' option). *Note
1680 absolute::, for more information about `--absolute-names'.
1682 If you give the name of a directory as either a file name or a member
1683 name, then `tar' acts recursively on all the files and directories
1684 beneath that directory. For example, the name `/' identifies all the
1685 files in the file system to `tar'.
1687 The distinction between file names and archive member names is
1688 especially important when shell globbing is used, and sometimes a
1689 source of confusion for newcomers. *Note wildcards::, for more
1690 information about globbing. The problem is that shells may only glob
1691 using existing files in the file system. Only `tar' itself may glob on
1692 archive members, so when needed, you must ensure that wildcard
1693 characters reach `tar' without being interpreted by the shell first.
1694 Using a backslash before `*' or `?', or putting the whole argument
1695 between quotes, is usually sufficient for this.
1697 Even if NAMEs are often specified on the command line, they can also
1698 be read from a text file in the file system, using the
1699 `--files-from=FILE-OF-NAMES' (`-T FILE-OF-NAMES') option.
1701 If you don't use any file name arguments, `--append' (`-r'),
1702 `--delete' and `--concatenate' (`--catenate', `-A') will do nothing,
1703 while `--create' (`-c') will usually yield a diagnostic and inhibit
1704 `tar' execution. The other operations of `tar' (`--list', `--extract',
1705 `--compare', and `--update') will act on the entire contents of the
1708 Besides successful exits, GNU `tar' may fail for many reasons. Some
1709 reasons correspond to bad usage, that is, when the `tar' command line
1710 is improperly written. Errors may be encountered later, while
1711 processing the archive or the files. Some errors are recoverable, in
1712 which case the failure is delayed until `tar' has completed all its
1713 work. Some errors are such that it would be not meaningful, or at
1714 least risky, to continue processing: `tar' then aborts processing
1715 immediately. All abnormal exits, whether immediate or delayed, should
1716 always be clearly diagnosed on `stderr', after a line stating the
1717 nature of the error.
1719 Possible exit codes of GNU `tar' are summarized in the following
1723 `Successful termination'.
1726 `Some files differ'. If tar was invoked with `--compare'
1727 (`--diff', `-d') command line option, this means that some files
1728 in the archive differ from their disk counterparts (*note
1729 compare::). If tar was given `--create', `--append' or `--update'
1730 option, this exit code means that some files were changed while
1731 being archived and so the resulting archive does not contain the
1732 exact copy of the file set.
1735 `Fatal error'. This means that some fatal, unrecoverable error
1738 If `tar' has invoked a subprocess and that subprocess exited with a
1739 nonzero exit code, `tar' exits with that code as well. This can
1740 happen, for example, if `tar' was given some compression option (*note
1741 gzip::) and the external compressor program failed. Another example is
1742 `rmt' failure during backup to the remote device (*note Remote Tape
1746 File: tar.info, Node: using tar options, Next: Styles, Prev: Synopsis, Up: tar invocation
1748 3.2 Using `tar' Options
1749 =======================
1751 GNU `tar' has a total of eight operating modes which allow you to
1752 perform a variety of tasks. You are required to choose one operating
1753 mode each time you employ the `tar' program by specifying one, and only
1754 one operation as an argument to the `tar' command (the corresponding
1755 options may be found at *note frequent operations:: and *note
1756 Operations::). Depending on circumstances, you may also wish to
1757 customize how the chosen operating mode behaves. For example, you may
1758 wish to change the way the output looks, or the format of the files
1759 that you wish to archive may require you to do something special in
1760 order to make the archive look right.
1762 You can customize and control `tar''s performance by running `tar'
1763 with one or more options (such as `--verbose' (`-v'), which we used in
1764 the tutorial). As we said in the tutorial, "options" are arguments to
1765 `tar' which are (as their name suggests) optional. Depending on the
1766 operating mode, you may specify one or more options. Different options
1767 will have different effects, but in general they all change details of
1768 the operation, such as archive format, archive name, or level of user
1769 interaction. Some options make sense with all operating modes, while
1770 others are meaningful only with particular modes. You will likely use
1771 some options frequently, while you will only use others infrequently, or
1772 not at all. (A full list of options is available in *note All
1775 The `TAR_OPTIONS' environment variable specifies default options to
1776 be placed in front of any explicit options. For example, if
1777 `TAR_OPTIONS' is `-v --unlink-first', `tar' behaves as if the two
1778 options `-v' and `--unlink-first' had been specified before any
1779 explicit options. Option specifications are separated by whitespace.
1780 A backslash escapes the next character, so it can be used to specify an
1781 option containing whitespace or a backslash.
1783 Note that `tar' options are case sensitive. For example, the
1784 options `-T' and `-t' are different; the first requires an argument for
1785 stating the name of a file providing a list of NAMEs, while the second
1786 does not require an argument and is another way to write `--list'
1789 In addition to the eight operations, there are many options to
1790 `tar', and three different styles for writing both: long (mnemonic)
1791 form, short form, and old style. These styles are discussed below.
1792 Both the options and the operations can be written in any of these three
1796 File: tar.info, Node: Styles, Next: All Options, Prev: using tar options, Up: tar invocation
1798 3.3 The Three Option Styles
1799 ===========================
1801 There are three styles for writing operations and options to the command
1802 line invoking `tar'. The different styles were developed at different
1803 times during the history of `tar'. These styles will be presented
1804 below, from the most recent to the oldest.
1806 Some options must take an argument(1). Where you _place_ the
1807 arguments generally depends on which style of options you choose. We
1808 will detail specific information relevant to each option style in the
1809 sections on the different option styles, below. The differences are
1810 subtle, yet can often be very important; incorrect option placement can
1811 cause you to overwrite a number of important files. We urge you to
1812 note these differences, and only use the option style(s) which makes
1813 the most sense to you until you feel comfortable with the others.
1815 Some options _may_ take an argument. Such options may have at most
1816 long and short forms, they do not have old style equivalent. The rules
1817 for specifying an argument for such options are stricter than those for
1818 specifying mandatory arguments. Please, pay special attention to them.
1822 * Long Options:: Long Option Style
1823 * Short Options:: Short Option Style
1824 * Old Options:: Old Option Style
1825 * Mixing:: Mixing Option Styles
1827 ---------- Footnotes ----------
1829 (1) For example, `--file' (`-f') takes the name of an archive file
1830 as an argument. If you do not supply an archive file name, `tar' will
1831 use a default, but this can be confusing; thus, we recommend that you
1832 always supply a specific archive file name.
1835 File: tar.info, Node: Long Options, Next: Short Options, Up: Styles
1837 3.3.1 Long Option Style
1838 -----------------------
1840 Each option has at least one "long" (or "mnemonic") name starting with
1841 two dashes in a row, e.g., `--list'. The long names are more clear than
1842 their corresponding short or old names. It sometimes happens that a
1843 single long option has many different names which are synonymous, such
1844 as `--compare' and `--diff'. In addition, long option names can be
1845 given unique abbreviations. For example, `--cre' can be used in place
1846 of `--create' because there is no other long option which begins with
1847 `cre'. (One way to find this out is by trying it and seeing what
1848 happens; if a particular abbreviation could represent more than one
1849 option, `tar' will tell you that that abbreviation is ambiguous and
1850 you'll know that that abbreviation won't work. You may also choose to
1851 run `tar --help' to see a list of options. Be aware that if you run
1852 `tar' with a unique abbreviation for the long name of an option you
1853 didn't want to use, you are stuck; `tar' will perform the command as
1856 Long options are meant to be obvious and easy to remember, and their
1857 meanings are generally easier to discern than those of their
1858 corresponding short options (see below). For example:
1860 $ tar --create --verbose --blocking-factor=20 --file=/dev/rmt0
1862 gives a fairly good set of hints about what the command does, even for
1863 those not fully acquainted with `tar'.
1865 Long options which require arguments take those arguments
1866 immediately following the option name. There are two ways of
1867 specifying a mandatory argument. It can be separated from the option
1868 name either by an equal sign, or by any amount of white space
1869 characters. For example, the `--file' option (which tells the name of
1870 the `tar' archive) is given a file such as `archive.tar' as argument by
1871 using any of the following notations: `--file=archive.tar' or `--file
1874 In contrast, optional arguments must always be introduced using an
1875 equal sign. For example, the `--backup' option takes an optional
1876 argument specifying backup type. It must be used as
1877 `--backup=BACKUP-TYPE'.
1880 File: tar.info, Node: Short Options, Next: Old Options, Prev: Long Options, Up: Styles
1882 3.3.2 Short Option Style
1883 ------------------------
1885 Most options also have a "short option" name. Short options start with
1886 a single dash, and are followed by a single character, e.g., `-t'
1887 (which is equivalent to `--list'). The forms are absolutely identical
1888 in function; they are interchangeable.
1890 The short option names are faster to type than long option names.
1892 Short options which require arguments take their arguments
1893 immediately following the option, usually separated by white space. It
1894 is also possible to stick the argument right after the short option
1895 name, using no intervening space. For example, you might write
1896 `-f archive.tar' or `-farchive.tar' instead of using
1897 `--file=archive.tar'. Both `--file=ARCHIVE-NAME' and `-f ARCHIVE-NAME'
1898 denote the option which indicates a specific archive, here named
1901 Short options which take optional arguments take their arguments
1902 immediately following the option letter, _without any intervening white
1905 Short options' letters may be clumped together, but you are not
1906 required to do this (as compared to old options; see below). When
1907 short options are clumped as a set, use one (single) dash for them all,
1908 e.g., ``tar' -cvf'. Only the last option in such a set is allowed to
1909 have an argument(1).
1911 When the options are separated, the argument for each option which
1912 requires an argument directly follows that option, as is usual for Unix
1913 programs. For example:
1915 $ tar -c -v -b 20 -f /dev/rmt0
1917 If you reorder short options' locations, be sure to move any
1918 arguments that belong to them. If you do not move the arguments
1919 properly, you may end up overwriting files.
1921 ---------- Footnotes ----------
1923 (1) Clustering many options, the last of which has an argument, is a
1924 rather opaque way to write options. Some wonder if GNU `getopt' should
1925 not even be made helpful enough for considering such usages as invalid.
1928 File: tar.info, Node: Old Options, Next: Mixing, Prev: Short Options, Up: Styles
1930 3.3.3 Old Option Style
1931 ----------------------
1933 Like short options, "old options" are single letters. However, old
1934 options must be written together as a single clumped set, without
1935 spaces separating them or dashes preceding them(1). This set of
1936 letters must be the first to appear on the command line, after the
1937 `tar' program name and some white space; old options cannot appear
1938 anywhere else. The letter of an old option is exactly the same letter
1939 as the corresponding short option. For example, the old option `t' is
1940 the same as the short option `-t', and consequently, the same as the
1941 long option `--list'. So for example, the command `tar cv' specifies
1942 the option `-v' in addition to the operation `-c'.
1944 When options that need arguments are given together with the command,
1945 all the associated arguments follow, in the same order as the options.
1946 Thus, the example given previously could also be written in the old
1949 $ tar cvbf 20 /dev/rmt0
1951 Here, `20' is the argument of `-b' and `/dev/rmt0' is the argument of
1954 On the other hand, this old style syntax makes it difficult to match
1955 option letters with their corresponding arguments, and is often
1956 confusing. In the command `tar cvbf 20 /dev/rmt0', for example, `20'
1957 is the argument for `-b', `/dev/rmt0' is the argument for `-f', and
1958 `-v' does not have a corresponding argument. Even using short options
1959 like in `tar -c -v -b 20 -f /dev/rmt0' is clearer, putting all
1960 arguments next to the option they pertain to.
1962 If you want to reorder the letters in the old option argument, be
1963 sure to reorder any corresponding argument appropriately.
1965 This old way of writing `tar' options can surprise even experienced
1966 users. For example, the two commands:
1968 tar cfz archive.tar.gz file
1969 tar -cfz archive.tar.gz file
1971 are quite different. The first example uses `archive.tar.gz' as the
1972 value for option `f' and recognizes the option `z'. The second
1973 example, however, uses `z' as the value for option `f' -- probably not
1976 Old options are kept for compatibility with old versions of `tar'.
1978 This second example could be corrected in many ways, among which the
1979 following are equivalent:
1981 tar -czf archive.tar.gz file
1982 tar -cf archive.tar.gz -z file
1983 tar cf archive.tar.gz -z file
1985 As far as we know, all `tar' programs, GNU and non-GNU, support old
1986 options. GNU `tar' supports them not only for historical reasons, but
1987 also because many people are used to them. For compatibility with Unix
1988 `tar', the first argument is always treated as containing command and
1989 option letters even if it doesn't start with `-'. Thus, `tar c' is
1990 equivalent to `tar -c': both of them specify the `--create' (`-c')
1991 command to create an archive.
1993 ---------- Footnotes ----------
1995 (1) Beware that if you precede options with a dash, you are
1996 announcing the short option style instead of the old option style;
1997 short options are decoded differently.
2000 File: tar.info, Node: Mixing, Prev: Old Options, Up: Styles
2002 3.3.4 Mixing Option Styles
2003 --------------------------
2005 All three styles may be intermixed in a single `tar' command, so long
2006 as the rules for each style are fully respected(1). Old style options
2007 and either of the modern styles of options may be mixed within a single
2008 `tar' command. However, old style options must be introduced as the
2009 first arguments only, following the rule for old options (old options
2010 must appear directly after the `tar' command and some white space).
2011 Modern options may be given only after all arguments to the old options
2012 have been collected. If this rule is not respected, a modern option
2013 might be falsely interpreted as the value of the argument to one of the
2016 For example, all the following commands are wholly equivalent, and
2017 illustrate the many combinations and orderings of option styles.
2019 tar --create --file=archive.tar
2020 tar --create -f archive.tar
2021 tar --create -farchive.tar
2022 tar --file=archive.tar --create
2023 tar --file=archive.tar -c
2024 tar -c --file=archive.tar
2025 tar -c -f archive.tar
2026 tar -c -farchive.tar
2029 tar -f archive.tar --create
2030 tar -f archive.tar -c
2031 tar -farchive.tar --create
2032 tar -farchive.tar -c
2033 tar c --file=archive.tar
2034 tar c -f archive.tar
2037 tar f archive.tar --create
2038 tar f archive.tar -c
2041 On the other hand, the following commands are _not_ equivalent to
2044 tar -f -c archive.tar
2050 These last examples mean something completely different from what the
2051 user intended (judging based on the example in the previous set which
2052 uses long options, whose intent is therefore very clear). The first
2053 four specify that the `tar' archive would be a file named `-c', `c',
2054 `carchive.tar' or `archive.tarc', respectively. The first two examples
2055 also specify a single non-option, NAME argument having the value
2056 `archive.tar'. The last example contains only old style option letters
2057 (repeating option `c' twice), not all of which are meaningful (eg., `.',
2058 `h', or `i'), with no argument value.
2060 ---------- Footnotes ----------
2062 (1) Before GNU `tar' version 1.11.6, a bug prevented intermixing old
2063 style options with long options in some cases.
2066 File: tar.info, Node: All Options, Next: help, Prev: Styles, Up: tar invocation
2068 3.4 All `tar' Options
2069 =====================
2071 The coming manual sections contain an alphabetical listing of all `tar'
2072 operations and options, with brief descriptions and cross-references to
2073 more in-depth explanations in the body of the manual. They also
2074 contain an alphabetically arranged table of the short option forms with
2075 their corresponding long option. You can use this table as a reference
2076 for deciphering `tar' commands in scripts.
2080 * Operation Summary::
2082 * Short Option Summary::
2085 File: tar.info, Node: Operation Summary, Next: Option Summary, Up: All Options
2092 Appends files to the end of the archive. *Note append::.
2096 Same as `--concatenate'. *Note concatenate::.
2100 Compares archive members with their counterparts in the file
2101 system, and reports differences in file size, mode, owner,
2102 modification date and contents. *Note compare::.
2106 Appends other `tar' archives to the end of the archive. *Note
2111 Creates a new `tar' archive. *Note create::.
2114 Deletes members from the archive. Don't try this on an archive on
2115 a tape! *Note delete::.
2119 Same `--compare'. *Note compare::.
2123 Extracts members from the archive into the file system. *Note
2128 Same as `--extract'. *Note extract::.
2132 Lists the members in an archive. *Note list::.
2136 Adds files to the end of the archive, but only if they are newer
2137 than their counterparts already in the archive, or if they do not
2138 already exist in the archive. *Note update::.
2142 File: tar.info, Node: Option Summary, Next: Short Option Summary, Prev: Operation Summary, Up: All Options
2149 Normally when creating an archive, `tar' strips an initial `/'
2150 from member names. This option disables that behavior. *Note
2154 (See `--newer', *note after::)
2157 A pattern must match an initial subsequence of the name's
2158 components. *Note controlling pattern-matching::.
2161 `--atime-preserve=replace'
2162 `--atime-preserve=system'
2163 Attempt to preserve the access time of files when reading them.
2164 This option currently is effective only on files that you own,
2165 unless you have superuser privileges.
2167 `--atime-preserve=replace' remembers the access time of a file
2168 before reading it, and then restores the access time afterwards.
2169 This may cause problems if other programs are reading the file at
2170 the same time, as the times of their accesses will be lost. On
2171 most platforms restoring the access time also requires `tar' to
2172 restore the data modification time too, so this option may also
2173 cause problems if other programs are writing the file at the same
2174 time (`tar' attempts to detect this situation, but cannot do so
2175 reliably due to race conditions). Worse, on most platforms
2176 restoring the access time also updates the status change time,
2177 which means that this option is incompatible with incremental
2180 `--atime-preserve=system' avoids changing time stamps on files,
2181 without interfering with time stamp updates caused by other
2182 programs, so it works better with incremental backups. However,
2183 it requires a special `O_NOATIME' option from the underlying
2184 operating and file system implementation, and it also requires
2185 that searching directories does not update their access times. As
2186 of this writing (November 2005) this works only with Linux, and
2187 only with Linux kernels 2.6.8 and later. Worse, there is
2188 currently no reliable way to know whether this feature actually
2189 works. Sometimes `tar' knows that it does not work, and if you use
2190 `--atime-preserve=system' then `tar' complains and exits right
2191 away. But other times `tar' might think that the option works
2192 when it actually does not.
2194 Currently `--atime-preserve' with no operand defaults to
2195 `--atime-preserve=replace', but this may change in the future as
2196 support for `--atime-preserve=system' improves.
2198 If your operating or file system does not support
2199 `--atime-preserve=system', you might be able to preserve access
2200 times reliably by using the `mount' command. For example, you can
2201 mount the file system read-only, or access the file system via a
2202 read-only loopback mount, or use the `noatime' mount option
2203 available on some systems. However, mounting typically requires
2204 superuser privileges and can be a pain to manage.
2208 During a `--create' operation, enables automatic compressed format
2209 recognition based on the archive suffix. The effect of this
2210 option is cancelled by `--no-auto-compress'. *Note gzip::.
2212 `--backup=BACKUP-TYPE'
2213 Rather than deleting files from the file system, `tar' will back
2214 them up using simple or numbered backups, depending upon
2215 BACKUP-TYPE. *Note backup::.
2219 With this option present, `tar' prints error messages for read
2220 errors with the block number in the archive file. *Note
2223 `--blocking-factor=BLOCKING'
2225 Sets the blocking factor `tar' uses to BLOCKING x 512 bytes per
2226 record. *Note Blocking Factor::.
2230 This option tells `tar' to read or write archives through `bzip2'.
2234 Check device numbers when creating a list of modified files for
2235 incremental archiving. This is the default. *Note device
2236 numbers::, for a detailed description.
2238 `--checkpoint[=NUMBER]'
2239 This option directs `tar' to print periodic checkpoint messages as
2240 it reads through the archive. It is intended for when you want a
2241 visual indication that `tar' is still running, but don't want to
2242 see `--verbose' output. You can also instruct `tar' to execute a
2243 list of actions on each checkpoint, see `--checkpoint-action'
2244 below. For a detailed description, see *note checkpoints::.
2246 `--checkpoint-action=ACTION'
2247 Instruct `tar' to execute an action upon hitting a breakpoint.
2248 Here we give only a brief outline. *Note checkpoints::, for a
2249 complete description.
2251 The ACTION argument can be one of the following:
2254 Produce an audible bell on the console.
2258 Print a single dot on the standard listing stream.
2261 Display a textual message on the standard error, with the
2262 status and number of the checkpoint. This is the default.
2265 Display STRING on the standard error. Before output, the
2266 string is subject to meta-character expansion.
2269 Execute the given COMMAND.
2272 Wait for TIME seconds.
2275 Output STRING on the current console (`/dev/tty').
2277 Several `--checkpoint-action' options can be specified. The
2278 supplied actions will be executed in order of their appearance in
2281 Using `--checkpoint-action' without `--checkpoint' assumes default
2282 checkpoint frequency of one checkpoint per 10 records.
2286 If this option was given, `tar' will check the number of links
2287 dumped for each processed file. If this number does not match the
2288 total number of hard links for the file, a warning message will be
2296 `tar' will use the `compress' program when reading or writing the
2297 archive. This allows you to directly act on archives while saving
2298 space. *Note gzip::.
2301 (See `--interactive'.) *Note interactive::.
2303 `--delay-directory-restore'
2304 Delay setting modification times and permissions of extracted
2305 directories until the end of extraction. *Note Directory
2306 Modification Times and Permissions::.
2310 When reading or writing a file to be archived, `tar' accesses the
2311 file that a symbolic link points to, rather than the symlink
2312 itself. *Note dereference::.
2316 When this option is specified, `tar' will change its current
2317 directory to DIR before performing any operations. When this
2318 option is used during archive creation, it is order sensitive.
2322 When performing operations, `tar' will skip files that match
2323 PATTERN. *Note exclude::.
2326 Exclude backup and lock files. *Note exclude-backups: exclude.
2328 `--exclude-from=FILE'
2330 Similar to `--exclude', except `tar' will use the list of patterns
2331 in the file FILE. *Note exclude::.
2334 Exclude from dump any directory containing a valid cache directory
2335 tag file, but still dump the directory node and the tag file
2338 *Note exclude-caches: exclude.
2340 `--exclude-caches-under'
2341 Exclude from dump any directory containing a valid cache directory
2342 tag file, but still dump the directory node itself.
2346 `--exclude-caches-all'
2347 Exclude from dump any directory containing a valid cache directory
2348 tag file. *Note exclude::.
2350 `--exclude-tag=FILE'
2351 Exclude from dump any directory containing file named FILE, but
2352 dump the directory node and FILE itself. *Note exclude-tag:
2355 `--exclude-tag-under=FILE'
2356 Exclude from dump the contents of any directory containing file
2357 named FILE, but dump the directory node itself. *Note
2358 exclude-tag-under: exclude.
2360 `--exclude-tag-all=FILE'
2361 Exclude from dump any directory containing file named FILE. *Note
2362 exclude-tag-all: exclude.
2365 Exclude from dump directories and files, that are internal for some
2366 widely used version control systems.
2368 *Note exclude-vcs: exclude.
2372 `tar' will use the file ARCHIVE as the `tar' archive it performs
2373 operations on, rather than `tar''s compilation dependent default.
2374 *Note file tutorial::.
2378 `tar' will use the contents of FILE as a list of archive members
2379 or files to operate on, in addition to those specified on the
2380 command-line. *Note files::.
2383 Forces `tar' to interpret the file name given to `--file' as a
2384 local file, even if it looks like a remote tape drive name. *Note
2385 local and remote archives::.
2389 Selects output archive format. FORMAT may be one of the following:
2392 Creates an archive that is compatible with Unix V7 `tar'.
2395 Creates an archive that is compatible with GNU `tar' version
2399 Creates archive in GNU tar 1.13 format. Basically it is the
2400 same as `oldgnu' with the only difference in the way it
2401 handles long numeric fields.
2404 Creates a POSIX.1-1988 compatible archive.
2407 Creates a POSIX.1-2001 archive.
2410 *Note Formats::, for a detailed discussion of these formats.
2413 This option instructs `tar' to print file times to their full
2414 resolution. Usually this means 1-second resolution, but that
2415 depends on the underlying file system. The `--full-time' option
2416 takes effect only when detailed output (verbosity level 2 or
2417 higher) has been requested using the `--verbose' option, e.g.,
2418 when listing or extracting archives:
2420 $ tar -t -v --full-time -f archive.tar
2422 or, when creating an archive:
2424 $ tar -c -vv --full-time -f archive.tar .
2426 Notice, thar when creating the archive you need to specify
2427 `--verbose' twice to get a detailed output (*note verbose
2431 Files added to the `tar' archive will have a group ID of GROUP,
2432 rather than the group from the source file. GROUP is first decoded
2433 as a group symbolic name, but if this interpretation fails, it has
2434 to be a decimal numeric group ID. *Note override::.
2436 Also see the comments for the `--owner=USER' option.
2442 This option tells `tar' to read or write archives through `gzip',
2443 allowing `tar' to directly operate on several kinds of compressed
2444 archives transparently. *Note gzip::.
2446 `--hard-dereference'
2447 When creating an archive, dereference hard links and store the
2448 files they refer to, instead of creating usual hard link members.
2454 `tar' will print out a short message summarizing the operations and
2455 options to `tar' and exit. *Note help::.
2458 Ignore case when matching member or file names with patterns.
2459 *Note controlling pattern-matching::.
2461 `--ignore-command-error'
2462 Ignore exit codes of subprocesses. *Note Writing to an External
2465 `--ignore-failed-read'
2466 Do not exit unsuccessfully merely because an unreadable file was
2467 encountered. *Note Reading::.
2471 With this option, `tar' will ignore zeroed blocks in the archive,
2472 which normally signals EOF. *Note Reading::.
2476 Informs `tar' that it is working with an old GNU-format
2477 incremental backup archive. It is intended primarily for
2478 backwards compatibility only. *Note Incremental Dumps::, for a
2479 detailed discussion of incremental archives.
2482 Send verbose output to FILE instead of to standard output.
2484 `--info-script=SCRIPT-FILE'
2485 `--new-volume-script=SCRIPT-FILE'
2487 When `tar' is performing multi-tape backups, SCRIPT-FILE is run at
2488 the end of each tape. If SCRIPT-FILE exits with nonzero status,
2489 `tar' fails immediately. *Note info-script::, for a detailed
2490 discussion of SCRIPT-FILE.
2495 Specifies that `tar' should ask the user for confirmation before
2496 performing potentially destructive options, such as overwriting
2497 files. *Note interactive::.
2499 `--keep-newer-files'
2500 Do not replace existing files that are newer than their archive
2501 copies when extracting files from an archive.
2505 Do not overwrite existing files when extracting files from an
2506 archive. *Note Keep Old Files::.
2510 When creating an archive, instructs `tar' to write NAME as a name
2511 record in the archive. When extracting or listing archives, `tar'
2512 will only operate on archives that have a label matching the
2513 pattern specified in NAME. *Note Tape Files::.
2516 Force incremental backup of level N. As of GNU `tar' version
2517 1.24, the option `--level=0' truncates the snapshot file, thereby
2518 forcing the level 0 dump. Other values of N are effectively
2519 ignored. *Note --level=0::, for details and examples.
2521 The use of this option is valid only in conjunction with the
2522 `--listed-incremental' option. *Note Incremental Dumps::, for a
2523 detailed description.
2525 `--listed-incremental=SNAPSHOT-FILE'
2527 During a `--create' operation, specifies that the archive that
2528 `tar' creates is a new GNU-format incremental backup, using
2529 SNAPSHOT-FILE to determine which files to backup. With other
2530 operations, informs `tar' that the archive is in incremental
2531 format. *Note Incremental Dumps::.
2534 This option tells `tar' to read or write archives through `lzip'.
2538 This option tells `tar' to read or write archives through `lzma'.
2542 This option tells `tar' to read or write archives through `lzop'.
2545 `--mode=PERMISSIONS'
2546 When adding files to an archive, `tar' will use PERMISSIONS for
2547 the archive members, rather than the permissions from the files.
2548 PERMISSIONS can be specified either as an octal number or as
2549 symbolic permissions, like with `chmod'. *Note override::.
2552 When adding files to an archive, `tar' will use DATE as the
2553 modification time of members when creating archives, instead of
2554 their actual modification times. The value of DATE can be either
2555 a textual date representation (*note Date input formats::) or a
2556 name of the existing file, starting with `/' or `.'. In the
2557 latter case, the modification time of that file is used. *Note
2562 Informs `tar' that it should create or otherwise operate on a
2563 multi-volume `tar' archive. *Note Using Multiple Tapes::.
2565 `--new-volume-script'
2566 (see `--info-script')
2571 When creating an archive, `tar' will only add files that have
2572 changed since DATE. If DATE begins with `/' or `.', it is taken
2573 to be the name of a file whose data modification time specifies
2574 the date. *Note after::.
2576 `--newer-mtime=DATE'
2577 Like `--newer', but add only files whose contents have changed (as
2578 opposed to just `--newer', which will also back up files for which
2579 any status information has changed). *Note after::.
2582 An exclude pattern can match any subsequence of the name's
2583 components. *Note controlling pattern-matching::.
2585 `--no-auto-compress'
2586 Disables automatic compressed format recognition based on the
2587 archive suffix. *Note --auto-compress::. *Note gzip::.
2590 Do not check device numbers when creating a list of modified files
2591 for incremental archiving. *Note device numbers::, for a detailed
2594 `--no-delay-directory-restore'
2595 Modification times and permissions of extracted directories are
2596 set when all files from this directory have been extracted. This
2597 is the default. *Note Directory Modification Times and
2601 Use case-sensitive matching. *Note controlling pattern-matching::.
2603 `--no-ignore-command-error'
2604 Print warnings about subprocesses that terminated with a nonzero
2605 exit code. *Note Writing to an External Program::.
2608 If the `--null' option was given previously, this option cancels
2609 its effect, so that any following `--files-from' options will
2610 expect their file lists to be newline-terminated.
2612 `--no-overwrite-dir'
2613 Preserve metadata of existing directories when extracting files
2614 from an archive. *Note Overwrite Old Files::.
2616 `--no-quote-chars=STRING'
2617 Remove characters listed in STRING from the list of quoted
2618 characters set by the previous `--quote-chars' option (*note
2622 With this option, `tar' will not recurse into directories. *Note
2627 When extracting an archive, do not attempt to preserve the owner
2628 specified in the `tar' archive. This the default behavior for
2631 `--no-same-permissions'
2632 When extracting an archive, subtract the user's umask from files
2633 from the permissions specified in the archive. This is the
2634 default behavior for ordinary users.
2637 The archive media does not support seeks to arbitrary locations.
2638 Usually `tar' determines automatically whether the archive can be
2639 seeked or not. Use this option to disable this mechanism.
2642 Treat all input file or member names literally, do not interpret
2643 escape sequences. *Note input name quoting::.
2646 Do not use wildcards. *Note controlling pattern-matching::.
2648 `--no-wildcards-match-slash'
2649 Wildcards do not match `/'. *Note controlling pattern-matching::.
2652 When `tar' is using the `--files-from' option, this option
2653 instructs `tar' to expect file names terminated with NUL, so `tar'
2654 can correctly work with file names that contain newlines. *Note
2658 This option will notify `tar' that it should use numeric user and
2659 group IDs when creating a `tar' file, rather than names. *Note
2663 The function of this option depends on the action `tar' is
2664 performing. When extracting files, `-o' is a synonym for
2665 `--no-same-owner', i.e., it prevents `tar' from restoring
2666 ownership of files being extracted.
2668 When creating an archive, it is a synonym for `--old-archive'.
2669 This behavior is for compatibility with previous versions of GNU
2670 `tar', and will be removed in future releases.
2672 *Note Changes::, for more information.
2674 `--occurrence[=NUMBER]'
2675 This option can be used in conjunction with one of the subcommands
2676 `--delete', `--diff', `--extract' or `--list' when a list of files
2677 is given either on the command line or via `-T' option.
2679 This option instructs `tar' to process only the NUMBERth
2680 occurrence of each named file. NUMBER defaults to 1, so
2682 tar -x -f archive.tar --occurrence filename
2684 will extract the first occurrence of the member `filename' from
2685 `archive.tar' and will terminate without scanning to the end of
2689 Synonym for `--format=v7'.
2692 Used when creating an archive. Prevents `tar' from recursing into
2693 directories that are on different file systems from the current
2697 Overwrite existing files and directory metadata when extracting
2698 files from an archive. *Note Overwrite Old Files::.
2701 Overwrite the metadata of existing directories when extracting
2702 files from an archive. *Note Overwrite Old Files::.
2705 Specifies that `tar' should use USER as the owner of members when
2706 creating archives, instead of the user associated with the source
2707 file. USER is first decoded as a user symbolic name, but if this
2708 interpretation fails, it has to be a decimal numeric user ID.
2711 This option does not affect extraction from archives.
2713 `--pax-option=KEYWORD-LIST'
2714 This option enables creation of the archive in POSIX.1-2001 format
2715 (*note posix::) and modifies the way `tar' handles the extended
2716 header keywords. KEYWORD-LIST is a comma-separated list of
2717 keyword options. *Note PAX keywords::, for a detailed discussion.
2721 Synonym for `--format=v7'.
2724 Same as `--format=posix'.
2727 Synonymous with specifying both `--preserve-permissions' and
2728 `--same-order'. *Note Setting Access Permissions::.
2731 (See `--same-order'; *note Reading::.)
2733 `--preserve-permissions'
2734 `--same-permissions'
2736 When `tar' is extracting an archive, it normally subtracts the
2737 users' umask from the permissions specified in the archive and uses
2738 that number as the permissions to create the destination file.
2739 Specifying this option instructs `tar' that it should use the
2740 permissions directly from the archive. *Note Setting Access
2743 `--quote-chars=STRING'
2744 Always quote characters from STRING, even if the selected quoting
2745 style would not quote them (*note quoting styles::).
2747 `--quoting-style=STYLE'
2748 Set quoting style to use when printing member and file names
2749 (*note quoting styles::). Valid STYLE values are: `literal',
2750 `shell', `shell-always', `c', `escape', `locale', and `clocale'.
2751 Default quoting style is `escape', unless overridden while
2752 configuring the package.
2754 `--read-full-records'
2756 Specifies that `tar' should reblock its input, for reading from
2757 pipes on systems with buggy implementations. *Note Reading::.
2759 `--record-size=SIZE[SUF]'
2760 Instructs `tar' to use SIZE bytes per record when accessing the
2761 archive. The argument can be suffixed with a "size suffix", e.g.
2762 `--record-size=10K' for 10 Kilobytes. *Note size-suffixes::, for
2763 a list of valid suffixes. *Note Blocking Factor::, for a detailed
2764 description of this option.
2767 With this option, `tar' recurses into directories (default).
2770 `--recursive-unlink'
2771 Remove existing directory hierarchies before extracting
2772 directories of the same name from the archive. *Note Recursive
2776 Directs `tar' to remove the source file from the file system after
2777 appending it to an archive. *Note remove files::.
2780 Disable use of some potentially harmful `tar' options. Currently
2781 this option disables shell invocation from multi-volume menu
2782 (*note Using Multiple Tapes::).
2785 Notifies `tar' that it should use CMD instead of the default
2786 `/usr/libexec/rmt' (*note Remote Tape Server::).
2789 Notifies `tar' that is should use CMD to communicate with remote
2790 devices. *Note Device::.
2795 This option is an optimization for `tar' when running on machines
2796 with small amounts of memory. It informs `tar' that the list of
2797 file arguments has already been sorted to match the order of files
2798 in the archive. *Note Reading::.
2801 When extracting an archive, `tar' will attempt to preserve the
2802 owner specified in the `tar' archive with this option present.
2803 This is the default behavior for the superuser; this option has an
2804 effect only for ordinary users. *Note Attributes::.
2806 `--same-permissions'
2807 (See `--preserve-permissions'; *note Setting Access Permissions::.)
2811 Assume that the archive media supports seeks to arbitrary
2812 locations. Usually `tar' determines automatically whether the
2813 archive can be seeked or not. This option is intended for use in
2814 cases when such recognition fails. It takes effect only if the
2815 archive is open for reading (e.g. with `--list' or `--extract'
2819 Displays the default options used by `tar' and exits successfully.
2820 This option is intended for use in shell scripts. Here is an
2821 example of what you can see using this option:
2823 $ tar --show-defaults
2824 --format=gnu -f- -b20 --quoting-style=escape
2825 --rmt-command=/usr/libexec/rmt --rsh-command=/usr/bin/rsh
2827 Notice, that this option outputs only one line. The example output
2828 above has been split to fit page boundaries.
2830 `--show-omitted-dirs'
2831 Instructs `tar' to mention the directories it is skipping when
2832 operating on a `tar' archive. *Note show-omitted-dirs::.
2834 `--show-transformed-names'
2835 `--show-stored-names'
2836 Display file or member names after applying any transformations
2837 (*note transform::). In particular, when used in conjunction with
2838 one of the archive creation operations it instructs `tar' to list
2839 the member names stored in the archive, as opposed to the actual
2840 file names. *Note listing member and file names::.
2844 Invokes a GNU extension when adding files to an archive that
2845 handles sparse files efficiently. *Note sparse::.
2847 `--sparse-version=VERSION'
2848 Specifies the "format version" to use when archiving sparse files.
2849 Implies `--sparse'. *Note sparse::. For the description of the
2850 supported sparse formats, *Note Sparse Formats::.
2852 `--starting-file=NAME'
2854 This option affects extraction only; `tar' will skip extracting
2855 files in the archive until it finds one that matches NAME. *Note
2858 `--strip-components=NUMBER'
2859 Strip given NUMBER of leading components from file names before
2860 extraction. For example, if archive `archive.tar' contained
2861 `/some/file/name', then running
2863 tar --extract --file archive.tar --strip-components=2
2865 would extract this file to file `name'.
2868 Alters the suffix `tar' uses when backing up files from the default
2869 `~'. *Note backup::.
2871 `--tape-length=NUM[SUF]'
2873 Specifies the length of tapes that `tar' is writing as being
2874 NUM x 1024 bytes long. If optional SUF is given, it specifies a
2875 multiplicative factor to be used instead of 1024. For example,
2876 `-L2M' means 2 megabytes. *Note size-suffixes::, for a list of
2877 allowed suffixes. *Note Using Multiple Tapes::, for a detailed
2878 discussion of this option.
2881 Reads the volume label. If an argument is specified, test whether
2882 it matches the volume label. *Note --test-label option::.
2884 `--to-command=COMMAND'
2885 During extraction `tar' will pipe extracted files to the standard
2886 input of COMMAND. *Note Writing to an External Program::.
2890 During extraction, `tar' will extract files to stdout rather than
2891 to the file system. *Note Writing to Standard Output::.
2894 Displays the total number of bytes transferred when processing an
2895 archive. If an argument is given, these data are displayed on
2896 request, when signal SIGNO is delivered to `tar'. *Note totals::.
2900 Sets the data modification time of extracted files to the
2901 extraction time, rather than the data modification time stored in
2902 the archive. *Note Data Modification Times::.
2904 `--transform=SED-EXPR'
2906 Transform file or member names using `sed' replacement expression
2907 SED-EXPR. For example,
2909 $ tar cf archive.tar --transform 's,^\./,usr/,' .
2911 will add to `archive' files from the current working directory,
2912 replacing initial `./' prefix with `usr/'. For the detailed
2913 discussion, *Note transform::.
2915 To see transformed member names in verbose listings, use
2916 `--show-transformed-names' option (*note show-transformed-names::).
2919 (See `--compress', *note gzip::)
2922 (See `--gzip', *note gzip::)
2926 Directs `tar' to remove the corresponding file from the file
2927 system before extracting it from the archive. *Note Unlink
2931 Enable unquoting input file or member names (default). *Note
2932 input name quoting::.
2934 `--use-compress-program=PROG'
2936 Instructs `tar' to access the archive through PROG, which is
2937 presumed to be a compression program of some sort. *Note gzip::.
2940 Display file modification dates in UTC. This option implies
2945 Specifies that `tar' should be more verbose about the operations
2946 it is performing. This option can be specified multiple times for
2947 some operations to increase the amount of information displayed.
2952 Verifies that the archive was correctly written when creating an
2953 archive. *Note verify::.
2956 Print information about the program's name, version, origin and
2957 legal status, all on standard output, and then exit successfully.
2961 Used in conjunction with `--multi-volume'. `tar' will keep track
2962 of which volume of a multi-volume archive it is working in FILE.
2966 Enable or disable warning messages identified by KEYWORD. The
2967 messages are suppressed if KEYWORD is prefixed with `no-'. *Note
2971 Use wildcards when matching member names with patterns. *Note
2972 controlling pattern-matching::.
2974 `--wildcards-match-slash'
2975 Wildcards match `/'. *Note controlling pattern-matching::.
2979 Use `xz' for compressing or decompressing the archives. *Note
2983 ---------- Footnotes ----------
2985 (1) Earlier versions of GNU `tar' understood `-l' as a synonym for
2986 `--one-file-system'. The current semantics, which complies to UNIX98,
2987 was introduced with version 1.15.91. *Note Changes::, for more
2991 File: tar.info, Node: Short Option Summary, Prev: Option Summary, Up: All Options
2993 3.4.3 Short Options Cross Reference
2994 -----------------------------------
2996 Here is an alphabetized list of all of the short option forms, matching
2997 them with the equivalent long option.
2999 Short Option Reference
3000 --------------------------------------------------------------------------
3001 -A *note --concatenate::.
3002 -B *note --read-full-records::.
3003 -C *note --directory::.
3004 -F *note --info-script::.
3005 -G *note --incremental::.
3007 -K *note --starting-file::.
3008 -L *note --tape-length::.
3009 -M *note --multi-volume::.
3011 -O *note --to-stdout::.
3012 -P *note --absolute-names::.
3013 -R *note --block-number::.
3014 -S *note --sparse::.
3015 -T *note --files-from::.
3016 -U *note --unlink-first::.
3018 -W *note --verify::.
3019 -X *note --exclude-from::.
3020 -Z *note --compress::.
3021 -b *note --blocking-factor::.
3022 -c *note --create::.
3023 -d *note --compare::.
3025 -g *note --listed-incremental::.
3026 -h *note --dereference::.
3027 -i *note --ignore-zeros::.
3029 -k *note --keep-old-files::.
3030 -l *note --check-links::.
3032 -o When creating, *note --no-same-owner::, when extracting --
3033 *note --portability::.
3035 The latter usage is deprecated. It is retained for
3036 compatibility with the earlier versions of GNU `tar'. In
3037 future releases `-o' will be equivalent to
3038 `--no-same-owner' only.
3039 -p *note --preserve-permissions::.
3040 -r *note --append::.
3041 -s *note --same-order::.
3043 -u *note --update::.
3044 -v *note --verbose::.
3045 -w *note --interactive::.
3046 -x *note --extract::.
3050 File: tar.info, Node: help, Next: defaults, Prev: All Options, Up: tar invocation
3052 3.5 GNU `tar' documentation
3053 ===========================
3055 Being careful, the first thing is really checking that you are using
3056 GNU `tar', indeed. The `--version' option causes `tar' to print
3057 information about its name, version, origin and legal status, all on
3058 standard output, and then exit successfully. For example,
3059 `tar --version' might print:
3062 Copyright (C) 2010 Free Software Foundation, Inc.
3063 Copyright (C) 2010 Free Software Foundation, Inc.
3064 License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
3065 This is free software: you are free to change and redistribute it.
3066 There is NO WARRANTY, to the extent permitted by law.
3068 Written by John Gilmore and Jay Fenlason.
3070 The first occurrence of `tar' in the result above is the program name
3071 in the package (for example, `rmt' is another program), while the
3072 second occurrence of `tar' is the name of the package itself,
3073 containing possibly many programs. The package is currently named
3074 `tar', after the name of the main program it contains(1).
3076 Another thing you might want to do is checking the spelling or
3077 meaning of some particular `tar' option, without resorting to this
3078 manual, for once you have carefully read it. GNU `tar' has a short
3079 help feature, triggerable through the `--help' option. By using this
3080 option, `tar' will print a usage message listing all available options
3081 on standard output, then exit successfully, without doing anything else
3082 and ignoring all other options. Even if this is only a brief summary,
3083 it may be several screens long. So, if you are not using some kind of
3084 scrollable window, you might prefer to use something like:
3088 presuming, here, that you like using `less' for a pager. Other popular
3089 pagers are `more' and `pg'. If you know about some KEYWORD which
3090 interests you and do not want to read all the `--help' output, another
3091 common idiom is doing:
3093 tar --help | grep KEYWORD
3095 for getting only the pertinent lines. Notice, however, that some `tar'
3096 options have long description lines and the above command will list
3097 only the first of them.
3099 The exact look of the option summary displayed by `tar --help' is
3100 configurable. *Note Configuring Help Summary::, for a detailed
3103 If you only wish to check the spelling of an option, running `tar
3104 --usage' may be a better choice. This will display a terse list of
3105 `tar' options without accompanying explanations.
3107 The short help output is quite succinct, and you might have to get
3108 back to the full documentation for precise points. If you are reading
3109 this paragraph, you already have the `tar' manual in some form. This
3110 manual is available in a variety of forms from
3111 `http://www.gnu.org/software/tar/manual'. It may be printed out of the
3112 GNU `tar' distribution, provided you have TeX already installed
3113 somewhere, and a laser printer around. Just configure the
3114 distribution, execute the command `make dvi', then print `doc/tar.dvi'
3115 the usual way (contact your local guru to know how). If GNU `tar' has
3116 been conveniently installed at your place, this manual is also
3117 available in interactive, hypertextual form as an Info file. Just call
3118 `info tar' or, if you do not have the `info' program handy, use the
3119 Info reader provided within GNU Emacs, calling `tar' from the main Info
3122 There is currently no `man' page for GNU `tar'. If you observe such
3123 a `man' page on the system you are running, either it does not belong
3124 to GNU `tar', or it has not been produced by GNU. Some package
3125 maintainers convert `tar --help' output to a man page, using
3126 `help2man'. In any case, please bear in mind that the authoritative
3127 source of information about GNU `tar' is this Texinfo documentation.
3129 ---------- Footnotes ----------
3131 (1) There are plans to merge the `cpio' and `tar' packages into a
3132 single one which would be called `paxutils'. So, who knows if, one of
3133 this days, the `--version' would not output `tar (GNU paxutils) 3.2'.
3136 File: tar.info, Node: defaults, Next: verbose, Prev: help, Up: tar invocation
3138 3.6 Obtaining GNU `tar' default values
3139 ======================================
3141 GNU `tar' has some predefined defaults that are used when you do not
3142 explicitly specify another values. To obtain a list of such defaults,
3143 use `--show-defaults' option. This will output the values in the form
3144 of `tar' command line options:
3146 $ tar --show-defaults
3147 --format=gnu -f- -b20 --quoting-style=escape
3148 --rmt-command=/etc/rmt --rsh-command=/usr/bin/rsh
3150 Notice, that this option outputs only one line. The example output
3151 above has been split to fit page boundaries.
3153 The above output shows that this version of GNU `tar' defaults to using
3154 `gnu' archive format (*note Formats::), it uses standard output as the
3155 archive, if no `--file' option has been given (*note file tutorial::),
3156 the default blocking factor is 20 (*note Blocking Factor::). It also
3157 shows the default locations where `tar' will look for `rmt' and `rsh'
3161 File: tar.info, Node: verbose, Next: checkpoints, Prev: defaults, Up: tar invocation
3163 3.7 Checking `tar' progress
3164 ===========================
3166 Typically, `tar' performs most operations without reporting any
3167 information to the user except error messages. When using `tar' with
3168 many options, particularly ones with complicated or
3169 difficult-to-predict behavior, it is possible to make serious mistakes.
3170 `tar' provides several options that make observing `tar' easier. These
3171 options cause `tar' to print information as it progresses in its job,
3172 and you might want to use them just for being more careful about what
3173 is going on, or merely for entertaining yourself. If you have
3174 encountered a problem when operating on an archive, however, you may
3175 need more information than just an error message in order to solve the
3176 problem. The following options can be helpful diagnostic tools.
3178 Normally, the `--list' (`-t') command to list an archive prints just
3179 the file names (one per line) and the other commands are silent. When
3180 used with most operations, the `--verbose' (`-v') option causes `tar'
3181 to print the name of each file or archive member as it is processed.
3182 This and the other options which make `tar' print status information
3183 can be useful in monitoring `tar'.
3185 With `--create' or `--extract', `--verbose' used once just prints
3186 the names of the files or members as they are processed. Using it
3187 twice causes `tar' to print a longer listing (*Note verbose member
3188 listing::, for the description) for each member. Since `--list'
3189 already prints the names of the members, `--verbose' used once with
3190 `--list' causes `tar' to print an `ls -l' type listing of the files in
3191 the archive. The following examples both extract members with long
3194 $ tar --extract --file=archive.tar --verbose --verbose
3195 $ tar xvvf archive.tar
3197 Verbose output appears on the standard output except when an archive
3198 is being written to the standard output, as with `tar --create --file=-
3199 --verbose' (`tar cfv -', or even `tar cv'--if the installer let
3200 standard output be the default archive). In that case `tar' writes
3201 verbose output to the standard error stream.
3203 If `--index-file=FILE' is specified, `tar' sends verbose output to
3204 FILE rather than to standard output or standard error.
3206 The `--totals' option causes `tar' to print on the standard error
3207 the total amount of bytes transferred when processing an archive. When
3208 creating or appending to an archive, this option prints the number of
3209 bytes written to the archive and the average speed at which they have
3212 $ tar -c -f archive.tar --totals /home
3213 Total bytes written: 7924664320 (7.4GiB, 85MiB/s)
3215 When reading an archive, this option displays the number of bytes
3218 $ tar -x -f archive.tar --totals
3219 Total bytes read: 7924664320 (7.4GiB, 95MiB/s)
3221 Finally, when deleting from an archive, the `--totals' option
3222 displays both numbers plus number of bytes removed from the archive:
3224 $ tar --delete -f foo.tar --totals --wildcards '*~'
3225 Total bytes read: 9543680 (9.2MiB, 201MiB/s)
3226 Total bytes written: 3829760 (3.7MiB, 81MiB/s)
3227 Total bytes deleted: 1474048
3229 You can also obtain this information on request. When `--totals' is
3230 used with an argument, this argument is interpreted as a symbolic name
3231 of a signal, upon delivery of which the statistics is to be printed:
3234 Print statistics upon delivery of signal SIGNO. Valid arguments
3235 are: `SIGHUP', `SIGQUIT', `SIGINT', `SIGUSR1' and `SIGUSR2'.
3236 Shortened names without `SIG' prefix are also accepted.
3238 Both forms of `--totals' option can be used simultaneously. Thus,
3239 `tar -x --totals --totals=USR1' instructs `tar' to extract all members
3240 from its default archive and print statistics after finishing the
3241 extraction, as well as when receiving signal `SIGUSR1'.
3243 The `--checkpoint' option prints an occasional message as `tar'
3244 reads or writes the archive. It is designed for those who don't need
3245 the more detailed (and voluminous) output of `--block-number' (`-R'),
3246 but do want visual confirmation that `tar' is actually making forward
3247 progress. By default it prints a message each 10 records read or
3248 written. This can be changed by giving it a numeric argument after an
3251 $ tar -c --checkpoint=1000 /var
3252 tar: Write checkpoint 1000
3253 tar: Write checkpoint 2000
3254 tar: Write checkpoint 3000
3256 This example shows the default checkpoint message used by `tar'. If
3257 you place a dot immediately after the equal sign, it will print a `.'
3258 at each checkpoint(1). For example:
3260 $ tar -c --checkpoint=.1000 /var
3263 The `--checkpoint' option provides a flexible mechanism for
3264 executing arbitrary actions upon hitting checkpoints, see the next
3265 section (*note checkpoints::), for more information on it.
3267 The `--show-omitted-dirs' option, when reading an archive--with
3268 `--list' or `--extract', for example--causes a message to be printed
3269 for each directory in the archive which is skipped. This happens
3270 regardless of the reason for skipping: the directory might not have
3271 been named on the command line (implicitly or explicitly), it might be
3272 excluded by the use of the `--exclude=PATTERN' option, or some other
3275 If `--block-number' (`-R') is used, `tar' prints, along with every
3276 message it would normally produce, the block number within the archive
3277 where the message was triggered. Also, supplementary messages are
3278 triggered when reading blocks full of NULs, or when hitting end of file
3279 on the archive. As of now, if the archive is properly terminated with
3280 a NUL block, the reading of the file may stop before end of file is
3281 met, so the position of end of file will not usually show when
3282 `--block-number' (`-R') is used. Note that GNU `tar' drains the
3283 archive before exiting when reading the archive from a pipe.
3285 This option is especially useful when reading damaged archives, since
3286 it helps pinpoint the damaged sections. It can also be used with
3287 `--list' (`-t') when listing a file-system backup tape, allowing you to
3288 choose among several backup tapes when retrieving a file later, in
3289 favor of the tape where the file appears earliest (closest to the front
3290 of the tape). *Note backup::.
3292 ---------- Footnotes ----------
3294 (1) This is actually a shortcut for `--checkpoint=N
3295 --checkpoint-action=dot'. *Note dot: checkpoints.
3298 File: tar.info, Node: checkpoints, Next: warnings, Prev: verbose, Up: tar invocation
3303 A "checkpoint" is a moment of time before writing Nth record to the
3304 archive (a "write checkpoint"), or before reading Nth record from the
3305 archive (a "read checkpoint"). Checkpoints allow to periodically
3306 execute arbitrary actions.
3308 The checkpoint facility is enabled using the following option:
3311 Schedule checkpoints before writing or reading each Nth record.
3312 The default value for N is 10.
3314 A list of arbitrary "actions" can be executed at each checkpoint.
3315 These actions include: pausing, displaying textual messages, and
3316 executing arbitrary external programs. Actions are defined using the
3317 `--checkpoint-action' option.
3319 `--checkpoint-action=ACTION'
3320 Execute an ACTION at each checkpoint.
3322 The simplest value of ACTION is `echo'. It instructs `tar' to
3323 display the default message on the standard error stream upon arriving
3324 at each checkpoint. The default message is (in POSIX locale) `Write
3325 checkpoint N', for write checkpoints, and `Read checkpoint N', for read
3326 checkpoints. Here, N represents ordinal number of the checkpoint.
3328 In another locales, translated versions of this message are used.
3330 This is the default action, so running:
3332 $ tar -c --checkpoint=1000 --checkpoint-action=echo /var
3336 $ tar -c --checkpoint=1000 /var
3338 The `echo' action also allows to supply a customized message. You
3339 do so by placing an equals sign and the message right after it, e.g.:
3341 --checkpoint-action="echo=Hit %s checkpoint #%u"
3343 The `%s' and `%u' in the above example are "meta-characters". The
3344 `%s' meta-character is replaced with the "type" of the checkpoint:
3345 `write' or `read' (or a corresponding translated version in locales
3346 other than POSIX). The `%u' meta-character is replaced with the
3347 ordinal number of the checkpoint. Thus, the above example could
3348 produce the following output when used with the `--create' option:
3350 tar: Hit write checkpoint #10
3351 tar: Hit write checkpoint #20
3352 tar: Hit write checkpoint #30
3354 Aside from meta-character expansion, the message string is subject to
3355 "unquoting", during which the backslash "escape sequences" are replaced
3356 with their corresponding ASCII characters (*note escape sequences::).
3357 E.g. the following action will produce an audible bell and the message
3358 described above at each checkpoint:
3360 --checkpoint-action='echo=\aHit %s checkpoint #%u'
3362 There is also a special action which produces an audible signal:
3363 `bell'. It is not equivalent to `echo='\a'', because `bell' sends the
3364 bell directly to the console (`/dev/tty'), whereas `echo='\a'' sends it
3365 to the standard error.
3367 The `ttyout=STRING' action outputs STRING to `/dev/tty', so it can
3368 be used even if the standard output is redirected elsewhere. The
3369 STRING is subject to the same modifications as with `echo' action. In
3370 contrast to the latter, `ttyout' does not prepend `tar' executable name
3371 to the string, nor does it output a newline after it. For example, the
3372 following action will print the checkpoint message at the same screen
3373 line, overwriting any previous message:
3375 --checkpoint-action="ttyout=\rHit %s checkpoint #%u"
3377 Another available checkpoint action is `dot' (or `.'). It instructs
3378 `tar' to print a single dot on the standard listing stream, e.g.:
3380 $ tar -c --checkpoint=1000 --checkpoint-action=dot /var
3383 For compatibility with previous GNU `tar' versions, this action can
3384 be abbreviated by placing a dot in front of the checkpoint frequency,
3385 as shown in the previous section.
3387 Yet another action, `sleep', pauses `tar' for a specified amount of
3388 seconds. The following example will stop for 30 seconds at each
3391 $ tar -c --checkpoint=1000 --checkpoint-action=sleep=30
3393 Finally, the `exec' action executes a given external program. For
3396 $ tar -c --checkpoint=1000 --checkpoint-action=exec=/sbin/cpoint
3398 This program is executed using `/bin/sh -c', with no additional
3399 arguments. Its exit code is ignored. It gets a copy of `tar''s
3400 environment plus the following variables:
3403 GNU `tar' version number.
3406 The name of the archive `tar' is processing.
3408 `TAR_BLOCKING_FACTOR'
3409 Current blocking factor (*note Blocking::).
3412 Number of the checkpoint.
3415 A short option describing the operation `tar' is executing. *Note
3416 Operations::, for a complete list of subcommand options.
3419 Format of the archive being processed. *Note Formats::, for a
3420 complete list of archive format names.
3422 Any number of actions can be defined, by supplying several
3423 `--checkpoint-action' options in the command line. For example, the
3424 command below displays two messages, pauses execution for 30 seconds
3425 and executes the `/sbin/cpoint' script:
3427 $ tar -c -f arc.tar \
3428 --checkpoint-action='\aecho=Hit %s checkpoint #%u' \
3429 --checkpoint-action='echo=Sleeping for 30 seconds' \
3430 --checkpoint-action='sleep=30' \
3431 --checkpoint-action='exec=/sbin/cpoint'
3433 This example also illustrates the fact that `--checkpoint-action'
3434 can be used without `--checkpoint'. In this case, the default
3435 checkpoint frequency (at each 10th record) is assumed.
3438 File: tar.info, Node: warnings, Next: interactive, Prev: checkpoints, Up: tar invocation
3440 3.9 Controlling Warning Messages
3441 ================================
3443 Sometimes, while performing the requested task, GNU `tar' notices some
3444 conditions that are not exactly errors, but which the user should be
3445 aware of. When this happens, `tar' issues a "warning message"
3446 describing the condition. Warning messages are output to the standard
3447 error and they do not affect the exit code of `tar' command.
3449 GNU `tar' allows the user to suppress some or all of its warning
3453 Control display of the warning messages identified by KEYWORD. If
3454 KEYWORD starts with the prefix `no-', such messages are
3455 suppressed. Otherwise, they are enabled.
3457 Multiple `--warning' messages accumulate.
3459 The tables below list allowed values for KEYWORD along with the
3460 warning messages they control.
3462 Keywords controlling `tar' operation
3463 ------------------------------------
3466 Enable all warning messages. This is the default.
3469 Disable all warning messages.
3472 `%s: file name read contains nul character'
3475 `A lone zero block at %s'
3477 Keywords applicable for `tar --create'
3478 --------------------------------------
3481 `%s: contains a cache directory tag %s; %s'
3484 `%s: File shrank by %s bytes; padding with zeros'
3487 `%s: file is on a different filesystem; not dumped'
3490 `%s: Unknown file type; file ignored'
3491 `%s: socket ignored'
3495 `%s: file is unchanged; not dumped'
3498 `%s: file is the archive; not dumped'
3501 `%s: File removed before we read it'
3504 `%s: file changed as we read it'
3506 Keywords applicable for `tar --extract'
3507 ---------------------------------------
3510 `%s: implausibly old time stamp %s'
3511 `%s: time stamp %s is %s s in the future'
3514 `Extracting contiguous files as regular files'
3517 `Attempting extraction of symbolic links as hard links'
3520 `%s: Unknown file type `%c', extracted as normal file'
3523 `Current %s is newer or same age'
3526 `Ignoring unknown extended header keyword `%s''
3528 Keywords controlling incremental extraction:
3529 --------------------------------------------
3532 `%s: Directory has been renamed from %s'
3533 `%s: Directory has been renamed'
3536 `%s: Directory is new'
3539 `%s: directory is on a different device: not purging'
3542 `Malformed dumpdir: 'X' never used'
3545 File: tar.info, Node: interactive, Prev: warnings, Up: tar invocation
3547 3.10 Asking for Confirmation During Operations
3548 ==============================================
3550 Typically, `tar' carries out a command without stopping for further
3551 instructions. In some situations however, you may want to exclude some
3552 files and archive members from the operation (for instance if disk or
3553 storage space is tight). You can do this by excluding certain files
3554 automatically (*note Choosing::), or by performing an operation
3555 interactively, using the `--interactive' (`-w') option. `tar' also
3556 accepts `--confirmation' for this option.
3558 When the `--interactive' (`-w') option is specified, before reading,
3559 writing, or deleting files, `tar' first prints a message for each such
3560 file, telling what operation it intends to take, then asks for
3561 confirmation on the terminal. The actions which require confirmation
3562 include adding a file to the archive, extracting a file from the
3563 archive, deleting a file from the archive, and deleting a file from
3564 disk. To confirm the action, you must type a line of input beginning
3565 with `y'. If your input line begins with anything other than `y',
3566 `tar' skips that file.
3568 If `tar' is reading the archive from the standard input, `tar' opens
3569 the file `/dev/tty' to support the interactive communications.
3571 Verbose output is normally sent to standard output, separate from
3572 other error messages. However, if the archive is produced directly on
3573 standard output, then verbose output is mixed with errors on `stderr'.
3574 Producing the archive on standard output may be used as a way to avoid
3575 using disk space, when the archive is soon to be consumed by another
3576 process reading it, say. Some people felt the need of producing an
3577 archive on stdout, still willing to segregate between verbose output
3578 and error output. A possible approach would be using a named pipe to
3579 receive the archive, and having the consumer process to read from that
3580 named pipe. This has the advantage of letting standard output free to
3581 receive verbose output, all separate from errors.
3584 File: tar.info, Node: operations, Next: Backups, Prev: tar invocation, Up: Top
3586 4 GNU `tar' Operations
3587 **********************
3600 File: tar.info, Node: Basic tar, Next: Advanced tar, Up: operations
3602 4.1 Basic GNU `tar' Operations
3603 ==============================
3605 The basic `tar' operations, `--create' (`-c'), `--list' (`-t') and
3606 `--extract' (`--get', `-x'), are currently presented and described in
3607 the tutorial chapter of this manual. This section provides some
3608 complementary notes for these operations.
3612 Creating an empty archive would have some kind of elegance. One
3613 can initialize an empty archive and later use `--append' (`-r')
3614 for adding all members. Some applications would not welcome
3615 making an exception in the way of adding the first archive member.
3616 On the other hand, many people reported that it is dangerously too
3617 easy for `tar' to destroy a magnetic tape with an empty
3618 archive(1). The two most common errors are:
3620 1. Mistakingly using `create' instead of `extract', when the
3621 intent was to extract the full contents of an archive. This
3622 error is likely: keys `c' and `x' are right next to each
3623 other on the QWERTY keyboard. Instead of being unpacked, the
3624 archive then gets wholly destroyed. When users speak about
3625 "exploding" an archive, they usually mean something else :-).
3627 2. Forgetting the argument to `file', when the intent was to
3628 create an archive with a single file in it. This error is
3629 likely because a tired user can easily add the `f' key to the
3630 cluster of option letters, by the mere force of habit,
3631 without realizing the full consequence of doing so. The
3632 usual consequence is that the single file, which was meant to
3633 be saved, is rather destroyed.
3635 So, recognizing the likelihood and the catastrophic nature of these
3636 errors, GNU `tar' now takes some distance from elegance, and
3637 cowardly refuses to create an archive when `--create' option is
3638 given, there are no arguments besides options, and `--files-from'
3639 (`-T') option is _not_ used. To get around the cautiousness of
3640 GNU `tar' and nevertheless create an archive with nothing in it,
3641 one may still use, as the value for the `--files-from' option, a
3642 file with no names in it, as shown in the following commands:
3644 tar --create --file=empty-archive.tar --files-from=/dev/null
3645 tar cfT empty-archive.tar /dev/null
3650 A socket is stored, within a GNU `tar' archive, as a pipe.
3653 GNU `tar' now shows dates as `1996-08-30', while it used to show
3654 them as `Aug 30 1996'. Preferably, people should get used to ISO
3655 8601 dates. Local American dates should be made available again
3656 with full date localization support, once ready. In the meantime,
3657 programs not being localizable for dates should prefer
3658 international dates, that's really the way to go.
3660 Look up `http://www.cl.cam.ac.uk/~mgk25/iso-time.html' if you are
3661 curious, it contains a detailed explanation of the ISO 8601
3665 ---------- Footnotes ----------
3667 (1) This is well described in `Unix-haters Handbook', by Simson
3668 Garfinkel, Daniel Weise & Steven Strassmann, IDG Books, ISBN
3672 File: tar.info, Node: Advanced tar, Next: create options, Prev: Basic tar, Up: operations
3674 4.2 Advanced GNU `tar' Operations
3675 =================================
3677 Now that you have learned the basics of using GNU `tar', you may want
3678 to learn about further ways in which `tar' can help you.
3680 This chapter presents five, more advanced operations which you
3681 probably won't use on a daily basis, but which serve more specialized
3682 functions. We also explain the different styles of options and why you
3683 might want to use one or another, or a combination of them in your `tar'
3684 commands. Additionally, this chapter includes options which allow you
3685 to define the output from `tar' more carefully, and provide help and
3686 error correction in special circumstances.
3698 File: tar.info, Node: Operations, Next: append, Up: Advanced tar
3700 4.2.1 The Five Advanced `tar' Operations
3701 ----------------------------------------
3703 In the last chapter, you learned about the first three operations to
3704 `tar'. This chapter presents the remaining five operations to `tar':
3705 `--append', `--update', `--concatenate', `--delete', and `--compare'.
3707 You are not likely to use these operations as frequently as those
3708 covered in the last chapter; however, since they perform specialized
3709 functions, they are quite useful when you do need to use them. We will
3710 give examples using the same directory and files that you created in
3711 the last chapter. As you may recall, the directory is called
3712 `practice', the files are `jazz', `blues', `folk', and the two archive
3713 files you created are `collection.tar' and `music.tar'.
3715 We will also use the archive files `afiles.tar' and `bfiles.tar'.
3716 The archive `afiles.tar' contains the members `apple', `angst', and
3717 `aspic'; `bfiles.tar' contains the members `./birds', `baboon', and
3720 Unless we state otherwise, all practicing you do and examples you
3721 follow in this chapter will take place in the `practice' directory that
3722 you created in the previous chapter; see *note prepare for examples::.
3723 (Below in this section, we will remind you of the state of the examples
3724 where the last chapter left them.)
3726 The five operations that we will cover in this chapter are:
3730 Add new entries to an archive that already exists.
3734 Add more recent copies of archive members to the end of an
3735 archive, if they exist.
3740 Add one or more pre-existing archives to the end of another
3744 Delete items from an archive (does not work on tapes).
3749 Compare archive members to their counterparts in the file system.
3752 File: tar.info, Node: append, Next: update, Prev: Operations, Up: Advanced tar
3754 4.2.2 How to Add Files to Existing Archives: `--append'
3755 -------------------------------------------------------
3757 If you want to add files to an existing archive, you don't need to
3758 create a new archive; you can use `--append' (`-r'). The archive must
3759 already exist in order to use `--append'. (A related operation is the
3760 `--update' operation; you can use this to add newer versions of archive
3761 members to an existing archive. To learn how to do this with
3762 `--update', *note update::.)
3764 If you use `--append' to add a file that has the same name as an
3765 archive member to an archive containing that archive member, then the
3766 old member is not deleted. What does happen, however, is somewhat
3767 complex. `tar' _allows_ you to have infinite number of files with the
3768 same name. Some operations treat these same-named members no
3769 differently than any other set of archive members: for example, if you
3770 view an archive with `--list' (`-t'), you will see all of those members
3771 listed, with their data modification times, owners, etc.
3773 Other operations don't deal with these members as perfectly as you
3774 might prefer; if you were to use `--extract' to extract the archive,
3775 only the most recently added copy of a member with the same name as
3776 other members would end up in the working directory. This is because
3777 `--extract' extracts an archive in the order the members appeared in
3778 the archive; the most recently archived members will be extracted last.
3779 Additionally, an extracted member will _replace_ a file of the same
3780 name which existed in the directory already, and `tar' will not prompt
3781 you about this(1). Thus, only the most recently archived member will
3782 end up being extracted, as it will replace the one extracted before it,
3785 There exists a special option that allows you to get around this
3786 behavior and extract (or list) only a particular copy of the file.
3787 This is `--occurrence' option. If you run `tar' with this option, it
3788 will extract only the first copy of the file. You may also give this
3789 option an argument specifying the number of copy to be extracted.
3790 Thus, for example if the archive `archive.tar' contained three copies
3791 of file `myfile', then the command
3793 tar --extract --file archive.tar --occurrence=2 myfile
3795 would extract only the second copy. *Note --occurrence: Option
3796 Summary, for the description of `--occurrence' option.
3798 If you want to replace an archive member, use `--delete' to delete
3799 the member you want to remove from the archive, and then use `--append'
3800 to add the member you want to be in the archive. Note that you can not
3801 change the order of the archive; the most recently added member will
3802 still appear last. In this sense, you cannot truly "replace" one
3803 member with another. (Replacing one member with another will not work
3804 on certain types of media, such as tapes; see *note delete:: and *note
3805 Media::, for more information.)
3809 * appending files:: Appending Files to an Archive
3812 ---------- Footnotes ----------
3814 (1) Unless you give it `--keep-old-files' option, or the disk copy
3815 is newer than the one in the archive and you invoke `tar' with
3816 `--keep-newer-files' option.
3819 File: tar.info, Node: appending files, Next: multiple, Up: append
3821 4.2.2.1 Appending Files to an Archive
3822 .....................................
3824 The simplest way to add a file to an already existing archive is the
3825 `--append' (`-r') operation, which writes specified files into the
3826 archive whether or not they are already among the archived files.
3828 When you use `--append', you _must_ specify file name arguments, as
3829 there is no default. If you specify a file that already exists in the
3830 archive, another copy of the file will be added to the end of the
3831 archive. As with other operations, the member names of the newly added
3832 files will be exactly the same as their names given on the command
3833 line. The `--verbose' (`-v') option will print out the names of the
3834 files as they are written into the archive.
3836 `--append' cannot be performed on some tape drives, unfortunately,
3837 due to deficiencies in the formats those tape drives use. The archive
3838 must be a valid `tar' archive, or else the results of using this
3839 operation will be unpredictable. *Note Media::.
3841 To demonstrate using `--append' to add a file to an archive, create
3842 a file called `rock' in the `practice' directory. Make sure you are in
3843 the `practice' directory. Then, run the following `tar' command to add
3844 `rock' to `collection.tar':
3846 $ tar --append --file=collection.tar rock
3848 If you now use the `--list' (`-t') operation, you will see that `rock'
3849 has been added to the archive:
3851 $ tar --list --file=collection.tar
3852 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
3853 -rw-r--r-- me user 21 1996-09-23 16:44 blues
3854 -rw-r--r-- me user 20 1996-09-23 16:44 folk
3855 -rw-r--r-- me user 20 1996-09-23 16:44 rock
3858 File: tar.info, Node: multiple, Prev: appending files, Up: append
3860 4.2.2.2 Multiple Members with the Same Name
3861 ...........................................
3863 You can use `--append' (`-r') to add copies of files which have been
3864 updated since the archive was created. (However, we do not recommend
3865 doing this since there is another `tar' option called `--update'; *Note
3866 update::, for more information. We describe this use of `--append'
3867 here for the sake of completeness.) When you extract the archive, the
3868 older version will be effectively lost. This works because files are
3869 extracted from an archive in the order in which they were archived.
3870 Thus, when the archive is extracted, a file archived later in time will
3871 replace a file of the same name which was archived earlier, even though
3872 the older version of the file will remain in the archive unless you
3873 delete all versions of the file.
3875 Supposing you change the file `blues' and then append the changed
3876 version to `collection.tar'. As you saw above, the original `blues' is
3877 in the archive `collection.tar'. If you change the file and append the
3878 new version of the file to the archive, there will be two copies in the
3879 archive. When you extract the archive, the older version of the file
3880 will be extracted first, and then replaced by the newer version when it
3883 You can append the new, changed copy of the file `blues' to the
3884 archive in this way:
3886 $ tar --append --verbose --file=collection.tar blues
3889 Because you specified the `--verbose' option, `tar' has printed the
3890 name of the file being appended as it was acted on. Now list the
3891 contents of the archive:
3893 $ tar --list --verbose --file=collection.tar
3894 -rw-r--r-- me user 28 1996-10-18 16:31 jazz
3895 -rw-r--r-- me user 21 1996-09-23 16:44 blues
3896 -rw-r--r-- me user 20 1996-09-23 16:44 folk
3897 -rw-r--r-- me user 20 1996-09-23 16:44 rock
3898 -rw-r--r-- me user 58 1996-10-24 18:30 blues
3900 The newest version of `blues' is now at the end of the archive (note
3901 the different creation dates and file sizes). If you extract the
3902 archive, the older version of the file `blues' will be replaced by the
3903 newer version. You can confirm this by extracting the archive and
3904 running `ls' on the directory.
3906 If you wish to extract the first occurrence of the file `blues' from
3907 the archive, use `--occurrence' option, as shown in the following
3910 $ tar --extract -vv --occurrence --file=collection.tar blues
3911 -rw-r--r-- me user 21 1996-09-23 16:44 blues
3913 *Note Writing::, for more information on `--extract' and see *note
3914 -occurrence: Option Summary, for a description of `--occurrence' option.
3917 File: tar.info, Node: update, Next: concatenate, Prev: append, Up: Advanced tar
3919 4.2.3 Updating an Archive
3920 -------------------------
3922 In the previous section, you learned how to use `--append' to add a
3923 file to an existing archive. A related operation is `--update' (`-u').
3924 The `--update' operation updates a `tar' archive by comparing the date
3925 of the specified archive members against the date of the file with the
3926 same name. If the file has been modified more recently than the
3927 archive member, then the newer version of the file is added to the
3928 archive (as with `--append').
3930 Unfortunately, you cannot use `--update' with magnetic tape drives.
3931 The operation will fail.
3933 Both `--update' and `--append' work by adding to the end of the
3934 archive. When you extract a file from the archive, only the version
3935 stored last will wind up in the file system, unless you use the
3936 `--backup' option. *Note multiple::, for a detailed discussion.
3943 File: tar.info, Node: how to update, Up: update
3945 4.2.3.1 How to Update an Archive Using `--update'
3946 .................................................
3948 You must use file name arguments with the `--update' (`-u') operation.
3949 If you don't specify any files, `tar' won't act on any files and won't
3950 tell you that it didn't do anything (which may end up confusing you).
3952 To see the `--update' option at work, create a new file,
3953 `classical', in your practice directory, and some extra text to the
3954 file `blues', using any text editor. Then invoke `tar' with the
3955 `update' operation and the `--verbose' (`-v') option specified, using
3956 the names of all the files in the `practice' directory as file name
3959 $ tar --update -v -f collection.tar blues folk rock classical
3964 Because we have specified verbose mode, `tar' prints out the names of
3965 the files it is working on, which in this case are the names of the
3966 files that needed to be updated. If you run `tar --list' and look at
3967 the archive, you will see `blues' and `classical' at its end. There
3968 will be a total of two versions of the member `blues'; the one at the
3969 end will be newer and larger, since you added text before updating it.
3971 The reason `tar' does not overwrite the older file when updating it
3972 is because writing to the middle of a section of tape is a difficult
3973 process. Tapes are not designed to go backward. *Note Media::, for
3974 more information about tapes.
3976 `--update' (`-u') is not suitable for performing backups for two
3977 reasons: it does not change directory content entries, and it lengthens
3978 the archive every time it is used. The GNU `tar' options intended
3979 specifically for backups are more efficient. If you need to run
3980 backups, please consult *note Backups::.
3983 File: tar.info, Node: concatenate, Next: delete, Prev: update, Up: Advanced tar
3985 4.2.4 Combining Archives with `--concatenate'
3986 ---------------------------------------------
3988 Sometimes it may be convenient to add a second archive onto the end of
3989 an archive rather than adding individual files to the archive. To add
3990 one or more archives to the end of another archive, you should use the
3991 `--concatenate' (`--catenate', `-A') operation.
3993 To use `--concatenate', give the first archive with `--file' option
3994 and name the rest of archives to be concatenated on the command line.
3995 The members, and their member names, will be copied verbatim from those
3996 archives to the first one(1). The new, concatenated archive will be
3997 called by the same name as the one given with the `--file' option. As
3998 usual, if you omit `--file', `tar' will use the value of the environment
3999 variable `TAPE', or, if this has not been set, the default archive name.
4001 To demonstrate how `--concatenate' works, create two small archives
4002 called `bluesrock.tar' and `folkjazz.tar', using the relevant files
4005 $ tar -cvf bluesrock.tar blues rock
4008 $ tar -cvf folkjazz.tar folk jazz
4012 If you like, You can run `tar --list' to make sure the archives contain
4013 what they are supposed to:
4015 $ tar -tvf bluesrock.tar
4016 -rw-r--r-- melissa user 105 1997-01-21 19:42 blues
4017 -rw-r--r-- melissa user 33 1997-01-20 15:34 rock
4018 $ tar -tvf jazzfolk.tar
4019 -rw-r--r-- melissa user 20 1996-09-23 16:44 folk
4020 -rw-r--r-- melissa user 65 1997-01-30 14:15 jazz
4022 We can concatenate these two archives with `tar':
4025 $ tar --concatenate --file=bluesrock.tar jazzfolk.tar
4027 If you now list the contents of the `bluesrock.tar', you will see
4028 that now it also contains the archive members of `jazzfolk.tar':
4030 $ tar --list --file=bluesrock.tar
4036 When you use `--concatenate', the source and target archives must
4037 already exist and must have been created using compatible format
4038 parameters. Notice, that `tar' does not check whether the archives it
4039 concatenates have compatible formats, it does not even check if the
4040 files are really tar archives.
4042 Like `--append' (`-r'), this operation cannot be performed on some
4043 tape drives, due to deficiencies in the formats those tape drives use.
4045 It may seem more intuitive to you to want or try to use `cat' to
4046 concatenate two archives instead of using the `--concatenate'
4047 operation; after all, `cat' is the utility for combining files.
4049 However, `tar' archives incorporate an end-of-file marker which must
4050 be removed if the concatenated archives are to be read properly as one
4051 archive. `--concatenate' removes the end-of-archive marker from the
4052 target archive before each new archive is appended. If you use `cat'
4053 to combine the archives, the result will not be a valid `tar' format
4054 archive. If you need to retrieve files from an archive that was added
4055 to using the `cat' utility, use the `--ignore-zeros' (`-i') option.
4056 *Note Ignore Zeros::, for further information on dealing with archives
4057 improperly combined using the `cat' shell utility.
4059 ---------- Footnotes ----------
4061 (1) This can cause multiple members to have the same name. For
4062 information on how this affects reading the archive, see *note
4066 File: tar.info, Node: delete, Next: compare, Prev: concatenate, Up: Advanced tar
4068 4.2.5 Removing Archive Members Using `--delete'
4069 -----------------------------------------------
4071 You can remove members from an archive by using the `--delete' option.
4072 Specify the name of the archive with `--file' (`-f') and then specify
4073 the names of the members to be deleted; if you list no member names,
4074 nothing will be deleted. The `--verbose' option will cause `tar' to
4075 print the names of the members as they are deleted. As with
4076 `--extract', you must give the exact member names when using `tar
4077 --delete'. `--delete' will remove all versions of the named file from
4078 the archive. The `--delete' operation can run very slowly.
4080 Unlike other operations, `--delete' has no short form.
4082 This operation will rewrite the archive. You can only use
4083 `--delete' on an archive if the archive device allows you to write to
4084 any point on the media, such as a disk; because of this, it does not
4085 work on magnetic tapes. Do not try to delete an archive member from a
4086 magnetic tape; the action will not succeed, and you will be likely to
4087 scramble the archive and damage your tape. There is no safe way
4088 (except by completely re-writing the archive) to delete files from most
4089 kinds of magnetic tape. *Note Media::.
4091 To delete all versions of the file `blues' from the archive
4092 `collection.tar' in the `practice' directory, make sure you are in that
4093 directory, and then,
4095 $ tar --list --file=collection.tar
4100 $ tar --delete --file=collection.tar blues
4101 $ tar --list --file=collection.tar
4106 The `--delete' option has been reported to work properly when `tar'
4107 acts as a filter from `stdin' to `stdout'.
4110 File: tar.info, Node: compare, Prev: delete, Up: Advanced tar
4112 4.2.6 Comparing Archive Members with the File System
4113 ----------------------------------------------------
4115 The `--compare' (`-d'), or `--diff' operation compares specified
4116 archive members against files with the same names, and then reports
4117 differences in file size, mode, owner, modification date and contents.
4118 You should _only_ specify archive member names, not file names. If you
4119 do not name any members, then `tar' will compare the entire archive.
4120 If a file is represented in the archive but does not exist in the file
4121 system, `tar' reports a difference.
4123 You have to specify the record size of the archive when modifying an
4124 archive with a non-default record size.
4126 `tar' ignores files in the file system that do not have
4127 corresponding members in the archive.
4129 The following example compares the archive members `rock', `blues'
4130 and `funk' in the archive `bluesrock.tar' with files of the same name
4131 in the file system. (Note that there is no file, `funk'; `tar' will
4132 report an error message.)
4134 $ tar --compare --file=bluesrock.tar rock blues funk
4137 tar: funk not found in archive
4139 The spirit behind the `--compare' (`--diff', `-d') option is to
4140 check whether the archive represents the current state of files on
4141 disk, more than validating the integrity of the archive media. For
4142 this latter goal, see *note verify::.
4145 File: tar.info, Node: create options, Next: extract options, Prev: Advanced tar, Up: operations
4147 4.3 Options Used by `--create'
4148 ==============================
4150 The previous chapter described the basics of how to use `--create'
4151 (`-c') to create an archive from a set of files. *Note create::. This
4152 section described advanced options to be used with `--create'.
4156 * override:: Overriding File Metadata.
4157 * Ignore Failed Read::
4160 File: tar.info, Node: override, Next: Ignore Failed Read, Up: create options
4162 4.3.1 Overriding File Metadata
4163 ------------------------------
4165 As described above, a `tar' archive keeps, for each member it contains,
4166 its "metadata", such as modification time, mode and ownership of the
4167 file. GNU `tar' allows to replace these data with other values when
4168 adding files to the archive. The options described in this section
4169 affect creation of archives of any type. For POSIX archives, see also
4170 *note PAX keywords::, for additional ways of controlling metadata,
4171 stored in the archive.
4173 `--mode=PERMISSIONS'
4174 When adding files to an archive, `tar' will use PERMISSIONS for
4175 the archive members, rather than the permissions from the files.
4176 PERMISSIONS can be specified either as an octal number or as
4177 symbolic permissions, like with `chmod' (*Note Permissions:
4178 (fileutils)File permissions. This reference also has useful
4179 information for those not being overly familiar with the UNIX
4180 permission system). Using latter syntax allows for more
4181 flexibility. For example, the value `a+rw' adds read and write
4182 permissions for everybody, while retaining executable bits on
4183 directories or on any other file already marked as executable:
4185 $ tar -c -f archive.tar --mode='a+rw' .
4188 When adding files to an archive, `tar' will use DATE as the
4189 modification time of members when creating archives, instead of
4190 their actual modification times. The argument DATE can be either
4191 a textual date representation in almost arbitrary format (*note
4192 Date input formats::) or a name of an existing file, starting with
4193 `/' or `.'. In the latter case, the modification time of that
4196 The following example will set the modification date to 00:00:00,
4199 $ tar -c -f archive.tar --mtime='1970-01-01' .
4201 When used with `--verbose' (*note verbose tutorial::) GNU `tar'
4202 will try to convert the specified date back to its textual
4203 representation and compare it with the one given with `--mtime'
4204 options. If the two dates differ, `tar' will print a warning
4205 saying what date it will use. This is to help user ensure he is
4206 using the right date.
4210 $ tar -c -f archive.tar -v --mtime=yesterday .
4211 tar: Option --mtime: Treating date `yesterday' as 2006-06-20
4216 Specifies that `tar' should use USER as the owner of members when
4217 creating archives, instead of the user associated with the source
4218 file. The argument USER can be either an existing user symbolic
4219 name, or a decimal numeric user ID.
4221 There is no value indicating a missing number, and `0' usually
4222 means `root'. Some people like to force `0' as the value to offer
4223 in their distributions for the owner of files, because the `root'
4224 user is anonymous anyway, so that might as well be the owner of
4225 anonymous archives. For example:
4227 $ tar -c -f archive.tar --owner=0 .
4231 $ tar -c -f archive.tar --owner=root .
4234 Files added to the `tar' archive will have a group ID of GROUP,
4235 rather than the group from the source file. The argument GROUP
4236 can be either an existing group symbolic name, or a decimal
4240 File: tar.info, Node: Ignore Failed Read, Prev: override, Up: create options
4242 4.3.2 Ignore Fail Read
4243 ----------------------
4245 `--ignore-failed-read'
4246 Do not exit with nonzero on unreadable files or directories.
4249 File: tar.info, Node: extract options, Next: backup, Prev: create options, Up: operations
4251 4.4 Options Used by `--extract'
4252 ===============================
4254 The previous chapter showed how to use `--extract' to extract an
4255 archive into the file system. Various options cause `tar' to extract
4256 more information than just file contents, such as the owner, the
4257 permissions, the modification date, and so forth. This section
4258 presents options to be used with `--extract' when certain special
4259 considerations arise. You may review the information presented in
4260 *note extract:: for more basic information about the `--extract'
4265 * Reading:: Options to Help Read Archives
4266 * Writing:: Changing How `tar' Writes Files
4267 * Scarce:: Coping with Scarce Resources
4270 File: tar.info, Node: Reading, Next: Writing, Up: extract options
4272 4.4.1 Options to Help Read Archives
4273 -----------------------------------
4275 Normally, `tar' will request data in full record increments from an
4276 archive storage device. If the device cannot return a full record,
4277 `tar' will report an error. However, some devices do not always return
4278 full records, or do not require the last record of an archive to be
4279 padded out to the next record boundary. To keep reading until you
4280 obtain a full record, or to accept an incomplete record if it contains
4281 an end-of-archive marker, specify the `--read-full-records' (`-B')
4282 option in conjunction with the `--extract' or `--list' operations.
4285 The `--read-full-records' (`-B') option is turned on by default when
4286 `tar' reads an archive from standard input, or from a remote machine.
4287 This is because on BSD Unix systems, attempting to read a pipe returns
4288 however much happens to be in the pipe, even if it is less than was
4289 requested. If this option were not enabled, `tar' would fail as soon
4290 as it read an incomplete record from the pipe.
4292 If you're not sure of the blocking factor of an archive, you can
4293 read the archive by specifying `--read-full-records' (`-B') and
4294 `--blocking-factor=512-SIZE' (`-b 512-SIZE'), using a blocking factor
4295 larger than what the archive uses. This lets you avoid having to
4296 determine the blocking factor of an archive. *Note Blocking Factor::.
4300 * read full records::
4304 File: tar.info, Node: read full records, Next: Ignore Zeros, Up: Reading
4306 Reading Full Records
4307 ....................
4309 `--read-full-records'
4312 Use in conjunction with `--extract' (`--get', `-x') to read an
4313 archive which contains incomplete records, or one which has a
4314 blocking factor less than the one specified.
4317 File: tar.info, Node: Ignore Zeros, Prev: read full records, Up: Reading
4319 Ignoring Blocks of Zeros
4320 ........................
4322 Normally, `tar' stops reading when it encounters a block of zeros
4323 between file entries (which usually indicates the end of the archive).
4324 `--ignore-zeros' (`-i') allows `tar' to completely read an archive
4325 which contains a block of zeros before the end (i.e., a damaged
4326 archive, or one that was created by concatenating several archives
4329 The `--ignore-zeros' (`-i') option is turned off by default because
4330 many versions of `tar' write garbage after the end-of-archive entry,
4331 since that part of the media is never supposed to be read. GNU `tar'
4332 does not write after the end of an archive, but seeks to maintain
4333 compatibility among archiving utilities.
4337 To ignore blocks of zeros (i.e., end-of-archive entries) which may
4338 be encountered while reading an archive. Use in conjunction with
4339 `--extract' or `--list'.
4342 File: tar.info, Node: Writing, Next: Scarce, Prev: Reading, Up: extract options
4344 4.4.2 Changing How `tar' Writes Files
4345 -------------------------------------
4347 _(This message will disappear, once this node revised.)_
4351 * Dealing with Old Files::
4352 * Overwrite Old Files::
4354 * Keep Newer Files::
4356 * Recursive Unlink::
4357 * Data Modification Times::
4358 * Setting Access Permissions::
4359 * Directory Modification Times and Permissions::
4360 * Writing to Standard Output::
4361 * Writing to an External Program::
4365 File: tar.info, Node: Dealing with Old Files, Next: Overwrite Old Files, Up: Writing
4367 Options Controlling the Overwriting of Existing Files
4368 .....................................................
4370 When extracting files, if `tar' discovers that the extracted file
4371 already exists, it normally replaces the file by removing it before
4372 extracting it, to prevent confusion in the presence of hard or symbolic
4373 links. (If the existing file is a symbolic link, it is removed, not
4374 followed.) However, if a directory cannot be removed because it is
4375 nonempty, `tar' normally overwrites its metadata (ownership,
4376 permission, etc.). The `--overwrite-dir' option enables this default
4377 behavior. To be more cautious and preserve the metadata of such a
4378 directory, use the `--no-overwrite-dir' option.
4380 To be even more cautious and prevent existing files from being
4381 replaced, use the `--keep-old-files' (`-k') option. It causes `tar' to
4382 refuse to replace or update a file that already exists, i.e., a file
4383 with the same name as an archive member prevents extraction of that
4384 archive member. Instead, it reports an error.
4386 To be more aggressive about altering existing files, use the
4387 `--overwrite' option. It causes `tar' to overwrite existing files and
4388 to follow existing symbolic links when extracting.
4390 Some people argue that GNU `tar' should not hesitate to overwrite
4391 files with other files when extracting. When extracting a `tar'
4392 archive, they expect to see a faithful copy of the state of the file
4393 system when the archive was created. It is debatable that this would
4394 always be a proper behavior. For example, suppose one has an archive
4395 in which `usr/local' is a link to `usr/local2'. Since then, maybe the
4396 site removed the link and renamed the whole hierarchy from
4397 `/usr/local2' to `/usr/local'. Such things happen all the time. I
4398 guess it would not be welcome at all that GNU `tar' removes the whole
4399 hierarchy just to make room for the link to be reinstated (unless it
4400 _also_ simultaneously restores the full `/usr/local2', of course!) GNU
4401 `tar' is indeed able to remove a whole hierarchy to reestablish a
4402 symbolic link, for example, but _only if_ `--recursive-unlink' is
4403 specified to allow this behavior. In any case, single files are
4406 Finally, the `--unlink-first' (`-U') option can improve performance
4407 in some cases by causing `tar' to remove files unconditionally before
4411 File: tar.info, Node: Overwrite Old Files, Next: Keep Old Files, Prev: Dealing with Old Files, Up: Writing
4417 Overwrite existing files and directory metadata when extracting
4418 files from an archive.
4420 This causes `tar' to write extracted files into the file system
4421 without regard to the files already on the system; i.e., files
4422 with the same names as archive members are overwritten when the
4423 archive is extracted. It also causes `tar' to extract the
4424 ownership, permissions, and time stamps onto any preexisting files
4425 or directories. If the name of a corresponding file name is a
4426 symbolic link, the file pointed to by the symbolic link will be
4427 overwritten instead of the symbolic link itself (if this is
4428 possible). Moreover, special devices, empty directories and even
4429 symbolic links are automatically removed if they are in the way of
4432 Be careful when using the `--overwrite' option, particularly when
4433 combined with the `--absolute-names' (`-P') option, as this
4434 combination can change the contents, ownership or permissions of
4435 any file on your system. Also, many systems do not take kindly to
4436 overwriting files that are currently being executed.
4439 Overwrite the metadata of directories when extracting files from an
4440 archive, but remove other files before extracting.
4443 File: tar.info, Node: Keep Old Files, Next: Keep Newer Files, Prev: Overwrite Old Files, Up: Writing
4450 Do not replace existing files from archive. The
4451 `--keep-old-files' (`-k') option prevents `tar' from replacing
4452 existing files with files with the same name from the archive. The
4453 `--keep-old-files' option is meaningless with `--list' (`-t').
4454 Prevents `tar' from replacing files in the file system during
4458 File: tar.info, Node: Keep Newer Files, Next: Unlink First, Prev: Keep Old Files, Up: Writing
4463 `--keep-newer-files'
4464 Do not replace existing files that are newer than their archive
4465 copies. This option is meaningless with `--list' (`-t').
4468 File: tar.info, Node: Unlink First, Next: Recursive Unlink, Prev: Keep Newer Files, Up: Writing
4475 Remove files before extracting over them. This can make `tar' run
4476 a bit faster if you know in advance that the extracted files all
4477 need to be removed. Normally this option slows `tar' down
4478 slightly, so it is disabled by default.
4481 File: tar.info, Node: Recursive Unlink, Next: Data Modification Times, Prev: Unlink First, Up: Writing
4486 `--recursive-unlink'
4487 When this option is specified, try removing files and directory
4488 hierarchies before extracting over them. _This is a dangerous
4491 If you specify the `--recursive-unlink' option, `tar' removes
4492 _anything_ that keeps you from extracting a file as far as current
4493 permissions will allow it. This could include removal of the contents
4494 of a full directory hierarchy.
4497 File: tar.info, Node: Data Modification Times, Next: Setting Access Permissions, Prev: Recursive Unlink, Up: Writing
4499 Setting Data Modification Times
4500 ...............................
4502 Normally, `tar' sets the data modification times of extracted files to
4503 the corresponding times recorded for the files in the archive, but
4504 limits the permissions of extracted files by the current `umask'
4507 To set the data modification times of extracted files to the time
4508 when the files were extracted, use the `--touch' (`-m') option in
4509 conjunction with `--extract' (`--get', `-x').
4513 Sets the data modification time of extracted archive members to
4514 the time they were extracted, not the time recorded for them in
4515 the archive. Use in conjunction with `--extract' (`--get', `-x').
4518 File: tar.info, Node: Setting Access Permissions, Next: Directory Modification Times and Permissions, Prev: Data Modification Times, Up: Writing
4520 Setting Access Permissions
4521 ..........................
4523 To set the modes (access permissions) of extracted files to those
4524 recorded for those files in the archive, use `--same-permissions' in
4525 conjunction with the `--extract' (`--get', `-x') operation.
4527 `--preserve-permissions'
4528 `--same-permissions'
4530 Set modes of extracted archive members to those recorded in the
4531 archive, instead of current umask settings. Use in conjunction
4532 with `--extract' (`--get', `-x').
4535 File: tar.info, Node: Directory Modification Times and Permissions, Next: Writing to Standard Output, Prev: Setting Access Permissions, Up: Writing
4537 Directory Modification Times and Permissions
4538 ............................................
4540 After successfully extracting a file member, GNU `tar' normally
4541 restores its permissions and modification times, as described in the
4542 previous sections. This cannot be done for directories, because after
4543 extracting a directory `tar' will almost certainly extract files into
4544 that directory and this will cause the directory modification time to
4545 be updated. Moreover, restoring that directory permissions may not
4546 permit file creation within it. Thus, restoring directory permissions
4547 and modification times must be delayed at least until all files have
4548 been extracted into that directory. GNU `tar' restores directories
4549 using the following approach.
4551 The extracted directories are created with the mode specified in the
4552 archive, as modified by the umask of the user, which gives sufficient
4553 permissions to allow file creation. The meta-information about the
4554 directory is recorded in the temporary list of directories. When
4555 preparing to extract next archive member, GNU `tar' checks if the
4556 directory prefix of this file contains the remembered directory. If it
4557 does not, the program assumes that all files have been extracted into
4558 that directory, restores its modification time and permissions and
4559 removes its entry from the internal list. This approach allows to
4560 correctly restore directory meta-information in the majority of cases,
4561 while keeping memory requirements sufficiently small. It is based on
4562 the fact, that most `tar' archives use the predefined order of members:
4563 first the directory, then all the files and subdirectories in that
4566 However, this is not always true. The most important exception are
4567 incremental archives (*note Incremental Dumps::). The member order in
4568 an incremental archive is reversed: first all directory members are
4569 stored, followed by other (non-directory) members. So, when extracting
4570 from incremental archives, GNU `tar' alters the above procedure. It
4571 remembers all restored directories, and restores their meta-data only
4572 after the entire archive has been processed. Notice, that you do not
4573 need to specify any special options for that, as GNU `tar'
4574 automatically detects archives in incremental format.
4576 There may be cases, when such processing is required for normal
4577 archives too. Consider the following example:
4579 $ tar --no-recursion -cvf archive \
4580 foo foo/file1 bar bar/file foo/file2
4587 During the normal operation, after encountering `bar' GNU `tar' will
4588 assume that all files from the directory `foo' were already extracted
4589 and will therefore restore its timestamp and permission bits. However,
4590 after extracting `foo/file2' the directory timestamp will be offset
4593 To correctly restore directory meta-information in such cases, use
4594 the `--delay-directory-restore' command line option:
4596 `--delay-directory-restore'
4597 Delays restoring of the modification times and permissions of
4598 extracted directories until the end of extraction. This way,
4599 correct meta-information is restored even if the archive has
4600 unusual member ordering.
4602 `--no-delay-directory-restore'
4603 Cancel the effect of the previous `--delay-directory-restore'.
4604 Use this option if you have used `--delay-directory-restore' in
4605 `TAR_OPTIONS' variable (*note TAR_OPTIONS::) and wish to
4606 temporarily disable it.
4609 File: tar.info, Node: Writing to Standard Output, Next: Writing to an External Program, Prev: Directory Modification Times and Permissions, Up: Writing
4611 Writing to Standard Output
4612 ..........................
4614 To write the extracted files to the standard output, instead of
4615 creating the files on the file system, use `--to-stdout' (`-O') in
4616 conjunction with `--extract' (`--get', `-x'). This option is useful if
4617 you are extracting files to send them through a pipe, and do not need to
4618 preserve them in the file system. If you extract multiple members,
4619 they appear on standard output concatenated, in the order they are
4620 found in the archive.
4624 Writes files to the standard output. Use only in conjunction with
4625 `--extract' (`--get', `-x'). When this option is used, instead of
4626 creating the files specified, `tar' writes the contents of the
4627 files extracted to its standard output. This may be useful if you
4628 are only extracting the files in order to send them through a
4629 pipe. This option is meaningless with `--list' (`-t').
4631 This can be useful, for example, if you have a tar archive containing
4632 a big file and don't want to store the file on disk before processing
4633 it. You can use a command like this:
4635 tar -xOzf foo.tgz bigfile | process
4637 or even like this if you want to process the concatenation of the
4640 tar -xOzf foo.tgz bigfile1 bigfile2 | process
4642 However, `--to-command' may be more convenient for use with multiple
4643 files. See the next section.
4646 File: tar.info, Node: Writing to an External Program, Next: remove files, Prev: Writing to Standard Output, Up: Writing
4648 Writing to an External Program
4649 ..............................
4651 You can instruct `tar' to send the contents of each extracted file to
4652 the standard input of an external program:
4654 `--to-command=COMMAND'
4655 Extract files and pipe their contents to the standard input of
4656 COMMAND. When this option is used, instead of creating the files
4657 specified, `tar' invokes COMMAND and pipes the contents of the
4658 files to its standard output. The COMMAND may contain command line
4659 arguments. The program is executed via `sh -c'. Notice, that
4660 COMMAND is executed once for each regular file extracted.
4661 Non-regular files (directories, etc.) are ignored when this option
4664 The command can obtain the information about the file it processes
4665 from the following environment variables:
4668 Type of the file. It is a single letter with the following meaning:
4677 Currently only regular files are supported.
4680 File mode, an octal number.
4683 The name of the file.
4686 Name of the file as stored in the archive.
4689 Name of the file owner.
4692 Name of the file owner group.
4695 Time of last access. It is a decimal number, representing seconds
4696 since the Epoch. If the archive provides times with nanosecond
4697 precision, the nanoseconds are appended to the timestamp after a
4701 Time of last modification.
4704 Time of last status change.
4710 UID of the file owner.
4713 GID of the file owner.
4715 Additionally, the following variables contain information about tar
4716 mode and the archive being processed:
4719 GNU `tar' version number.
4722 The name of the archive `tar' is processing.
4724 `TAR_BLOCKING_FACTOR'
4725 Current blocking factor (*note Blocking::).
4728 Ordinal number of the volume `tar' is processing.
4731 Format of the archive being processed. *Note Formats::, for a
4732 complete list of archive format names.
4734 If COMMAND exits with a non-0 status, `tar' will print an error
4735 message similar to the following:
4737 tar: 2345: Child returned status 1
4739 Here, `2345' is the PID of the finished process.
4741 If this behavior is not wanted, use `--ignore-command-error':
4743 `--ignore-command-error'
4744 Ignore exit codes of subprocesses. Notice that if the program
4745 exits on signal or otherwise terminates abnormally, the error
4746 message will be printed even if this option is used.
4748 `--no-ignore-command-error'
4749 Cancel the effect of any previous `--ignore-command-error' option.
4750 This option is useful if you have set `--ignore-command-error' in
4751 `TAR_OPTIONS' (*note TAR_OPTIONS::) and wish to temporarily cancel
4755 File: tar.info, Node: remove files, Prev: Writing to an External Program, Up: Writing
4761 Remove files after adding them to the archive.
4764 File: tar.info, Node: Scarce, Prev: Writing, Up: extract options
4766 4.4.3 Coping with Scarce Resources
4767 ----------------------------------
4769 _(This message will disappear, once this node revised.)_
4777 File: tar.info, Node: Starting File, Next: Same Order, Up: Scarce
4782 `--starting-file=NAME'
4784 Starts an operation in the middle of an archive. Use in
4785 conjunction with `--extract' (`--get', `-x') or `--list' (`-t').
4787 If a previous attempt to extract files failed due to lack of disk
4788 space, you can use `--starting-file=NAME' (`-K NAME') to start
4789 extracting only after member NAME of the archive. This assumes, of
4790 course, that there is now free space, or that you are now extracting
4791 into a different file system. (You could also choose to suspend `tar',
4792 remove unnecessary files from the file system, and then resume the same
4793 `tar' operation. In this case, `--starting-file' is not necessary.)
4794 See also *note interactive::, and *note exclude::.
4797 File: tar.info, Node: Same Order, Prev: Starting File, Up: Scarce
4805 To process large lists of file names on machines with small
4806 amounts of memory. Use in conjunction with `--compare' (`--diff',
4807 `-d'), `--list' (`-t') or `--extract' (`--get', `-x').
4809 The `--same-order' (`--preserve-order', `-s') option tells `tar'
4810 that the list of file names to be listed or extracted is sorted in the
4811 same order as the files in the archive. This allows a large list of
4812 names to be used, even on a small machine that would not otherwise be
4813 able to hold all the names in memory at the same time. Such a sorted
4814 list can easily be created by running `tar -t' on the archive and
4817 This option is probably never needed on modern computer systems.
4820 File: tar.info, Node: backup, Next: Applications, Prev: extract options, Up: operations
4825 GNU `tar' offers options for making backups of files before writing new
4826 versions. These options control the details of these backups. They
4827 may apply to the archive itself before it is created or rewritten, as
4828 well as individual extracted members. Other GNU programs (`cp',
4829 `install', `ln', and `mv', for example) offer similar options.
4831 Backup options may prove unexpectedly useful when extracting archives
4832 containing many members having identical name, or when extracting
4833 archives on systems having file name limitations, making different
4834 members appear as having similar names through the side-effect of name
4837 When any existing file is backed up before being overwritten by
4838 extraction, then clashing files are automatically be renamed to be
4839 unique, and the true name is kept for only the last file of a series of
4840 clashing files. By using verbose mode, users may track exactly what
4843 At the detail level, some decisions are still experimental, and may
4844 change in the future, we are waiting comments from our users. So,
4845 please do not learn to depend blindly on the details of the backup
4846 features. For example, currently, directories themselves are never
4847 renamed through using these options, so, extracting a file over a
4848 directory still has good chances to fail. Also, backup options apply
4849 to created archives, not only to extracted members. For created
4850 archives, backups will not be attempted when the archive is a block or
4851 character device, or when it refers to a remote file.
4853 For the sake of simplicity and efficiency, backups are made by
4854 renaming old files prior to creation or extraction, and not by copying.
4855 The original name is restored if the file creation fails. If a failure
4856 occurs after a partial extraction of a file, both the backup and the
4857 partially extracted file are kept.
4860 Back up files that are about to be overwritten or removed.
4861 Without this option, the original versions are destroyed.
4863 Use METHOD to determine the type of backups made. If METHOD is
4864 not specified, use the value of the `VERSION_CONTROL' environment
4865 variable. And if `VERSION_CONTROL' is not set, use the `existing'
4868 This option corresponds to the Emacs variable `version-control';
4869 the same values for METHOD are accepted as in Emacs. This option
4870 also allows more descriptive names. The valid METHODs are:
4874 Always make numbered backups.
4878 Make numbered backups of files that already have them, simple
4879 backups of the others.
4883 Always make simple backups.
4887 Append SUFFIX to each backup file made with `--backup'. If this
4888 option is not specified, the value of the `SIMPLE_BACKUP_SUFFIX'
4889 environment variable is used. And if `SIMPLE_BACKUP_SUFFIX' is not
4890 set, the default is `~', just as in Emacs.
4894 File: tar.info, Node: Applications, Next: looking ahead, Prev: backup, Up: operations
4896 4.6 Notable `tar' Usages
4897 ========================
4899 _(This message will disappear, once this node revised.)_
4901 You can easily use archive files to transport a group of files from one
4902 system to another: put all relevant files into an archive on one
4903 computer system, transfer the archive to another system, and extract
4904 the contents there. The basic transfer medium might be magnetic tape,
4905 Internet FTP, or even electronic mail (though you must encode the
4906 archive with `uuencode' in order to transport it properly by mail).
4907 Both machines do not have to use the same operating system, as long as
4908 they both support the `tar' program.
4910 For example, here is how you might copy a directory's contents from
4911 one disk to another, while preserving the dates, modes, owners and
4912 link-structure of all the files therein. In this case, the transfer
4915 $ (cd sourcedir; tar -cf - .) | (cd targetdir; tar -xf -)
4917 You can avoid subshells by using `-C' option:
4919 $ tar -C sourcedir -cf - . | tar -C targetdir -xf -
4921 The command also works using long option forms:
4923 $ (cd sourcedir; tar --create --file=- . ) \
4924 | (cd targetdir; tar --extract --file=-)
4928 $ tar --directory sourcedir --create --file=- . \
4929 | tar --directory targetdir --extract --file=-
4931 This is one of the easiest methods to transfer a `tar' archive.
4934 File: tar.info, Node: looking ahead, Prev: Applications, Up: operations
4936 4.7 Looking Ahead: The Rest of this Manual
4937 ==========================================
4939 You have now seen how to use all eight of the operations available to
4940 `tar', and a number of the possible options. The next chapter explains
4941 how to choose and change file and archive names, how to use files to
4942 store names of other files which you can then call as arguments to
4943 `tar' (this can help you save time if you expect to archive the same
4944 list of files a number of times), and so forth.
4946 If there are too many files to conveniently list on the command line,
4947 you can list the names in a file, and `tar' will read that file. *Note
4950 There are various ways of causing `tar' to skip over some files, and
4951 not archive them. *Note Choosing::.
4954 File: tar.info, Node: Backups, Next: Choosing, Prev: operations, Up: Top
4956 5 Performing Backups and Restoring Files
4957 ****************************************
4959 GNU `tar' is distributed along with the scripts for performing backups
4960 and restores. Even if there is a good chance those scripts may be
4961 satisfying to you, they are not the only scripts or methods available
4962 for doing backups and restore. You may well create your own, or use
4963 more sophisticated packages dedicated to that purpose.
4965 Some users are enthusiastic about `Amanda' (The Advanced Maryland
4966 Automatic Network Disk Archiver), a backup system developed by James da
4967 Silva `jds@cs.umd.edu' and available on many Unix systems. This is
4968 free software, and it is available from `http://www.amanda.org'.
4970 This chapter documents both the provided shell scripts and `tar'
4971 options which are more specific to usage as a backup tool.
4973 To "back up" a file system means to create archives that contain all
4974 the files in that file system. Those archives can then be used to
4975 restore any or all of those files (for instance if a disk crashes or a
4976 file is accidentally deleted). File system "backups" are also called
4981 * Full Dumps:: Using `tar' to Perform Full Dumps
4982 * Incremental Dumps:: Using `tar' to Perform Incremental Dumps
4983 * Backup Levels:: Levels of Backups
4984 * Backup Parameters:: Setting Parameters for Backups and Restoration
4985 * Scripted Backups:: Using the Backup Scripts
4986 * Scripted Restoration:: Using the Restore Script
4989 File: tar.info, Node: Full Dumps, Next: Incremental Dumps, Up: Backups
4991 5.1 Using `tar' to Perform Full Dumps
4992 =====================================
4994 _(This message will disappear, once this node revised.)_
4996 Full dumps should only be made when no other people or programs are
4997 modifying files in the file system. If files are modified while `tar'
4998 is making the backup, they may not be stored properly in the archive,
4999 in which case you won't be able to restore them if you have to. (Files
5000 not being modified are written with no trouble, and do not corrupt the
5003 You will want to use the `--label=ARCHIVE-LABEL' (`-V
5004 ARCHIVE-LABEL') option to give the archive a volume label, so you can
5005 tell what this archive is even if the label falls off the tape, or
5008 Unless the file system you are dumping is guaranteed to fit on one
5009 volume, you will need to use the `--multi-volume' (`-M') option. Make
5010 sure you have enough tapes on hand to complete the backup.
5012 If you want to dump each file system separately you will need to use
5013 the `--one-file-system' option to prevent `tar' from crossing file
5014 system boundaries when storing (sub)directories.
5016 The `--incremental' (`-G') (*note Incremental Dumps::) option is not
5017 needed, since this is a complete copy of everything in the file system,
5018 and a full restore from this backup would only be done onto a completely
5021 Unless you are in a hurry, and trust the `tar' program (and your
5022 tapes), it is a good idea to use the `--verify' (`-W') option, to make
5023 sure your files really made it onto the dump properly. This will also
5024 detect cases where the file was modified while (or just after) it was
5025 being archived. Not all media (notably cartridge tapes) are capable of
5026 being verified, unfortunately.
5029 File: tar.info, Node: Incremental Dumps, Next: Backup Levels, Prev: Full Dumps, Up: Backups
5031 5.2 Using `tar' to Perform Incremental Dumps
5032 ============================================
5034 "Incremental backup" is a special form of GNU `tar' archive that stores
5035 additional metadata so that exact state of the file system can be
5036 restored when extracting the archive.
5038 GNU `tar' currently offers two options for handling incremental
5039 backups: `--listed-incremental=SNAPSHOT-FILE' (`-g SNAPSHOT-FILE') and
5040 `--incremental' (`-G').
5042 The option `--listed-incremental' instructs tar to operate on an
5043 incremental archive with additional metadata stored in a standalone
5044 file, called a "snapshot file". The purpose of this file is to help
5045 determine which files have been changed, added or deleted since the
5046 last backup, so that the next incremental backup will contain only
5047 modified files. The name of the snapshot file is given as an argument
5050 `--listed-incremental=FILE'
5052 Handle incremental backups with snapshot data in FILE.
5054 To create an incremental backup, you would use
5055 `--listed-incremental' together with `--create' (*note create::). For
5059 --file=archive.1.tar \
5060 --listed-incremental=/var/log/usr.snar \
5063 This will create in `archive.1.tar' an incremental backup of the
5064 `/usr' file system, storing additional metadata in the file
5065 `/var/log/usr.snar'. If this file does not exist, it will be created.
5066 The created archive will then be a "level 0 backup"; please see the
5067 next section for more on backup levels.
5069 Otherwise, if the file `/var/log/usr.snar' exists, it determines
5070 which files are modified. In this case only these files will be stored
5071 in the archive. Suppose, for example, that after running the above
5072 command, you delete file `/usr/doc/old' and create directory
5073 `/usr/local/db' with the following contents:
5079 Some time later you create another incremental backup. You will
5083 --file=archive.2.tar \
5084 --listed-incremental=/var/log/usr.snar \
5086 tar: usr/local/db: Directory is new
5091 The created archive `archive.2.tar' will contain only these three
5092 members. This archive is called a "level 1 backup". Notice that
5093 `/var/log/usr.snar' will be updated with the new data, so if you plan
5094 to create more `level 1' backups, it is necessary to create a working
5095 copy of the snapshot file before running `tar'. The above example will
5096 then be modified as follows:
5098 $ cp /var/log/usr.snar /var/log/usr.snar-1
5100 --file=archive.2.tar \
5101 --listed-incremental=/var/log/usr.snar-1 \
5104 You can force `level 0' backups either by removing the snapshot file
5105 before running `tar', or by supplying the `--level=0' option, e.g.:
5108 --file=archive.2.tar \
5109 --listed-incremental=/var/log/usr.snar-0 \
5113 Incremental dumps depend crucially on time stamps, so the results are
5114 unreliable if you modify a file's time stamps during dumping (e.g.,
5115 with the `--atime-preserve=replace' option), or if you set the clock
5118 Metadata stored in snapshot files include device numbers, which,
5119 obviously are supposed to be non-volatile values. However, it turns
5120 out that NFS devices have undependable values when an automounter gets
5121 in the picture. This can lead to a great deal of spurious redumping in
5122 incremental dumps, so it is somewhat useless to compare two NFS devices
5123 numbers over time. The solution implemented currently is to consider
5124 all NFS devices as being equal when it comes to comparing directories;
5125 this is fairly gross, but there does not seem to be a better way to go.
5127 Apart from using NFS, there are a number of cases where relying on
5128 device numbers can cause spurious redumping of unmodified files. For
5129 example, this occurs when archiving LVM snapshot volumes. To avoid
5130 this, use `--no-check-device' option:
5133 Do not rely on device numbers when preparing a list of changed
5134 files for an incremental dump.
5137 Use device numbers when preparing a list of changed files for an
5138 incremental dump. This is the default behavior. The purpose of
5139 this option is to undo the effect of the `--no-check-device' if it
5140 was given in `TAR_OPTIONS' environment variable (*note
5143 There is also another way to cope with changing device numbers. It
5144 is described in detail in *note Fixing Snapshot Files::.
5146 Note that incremental archives use `tar' extensions and may not be
5147 readable by non-GNU versions of the `tar' program.
5149 To extract from the incremental dumps, use `--listed-incremental'
5150 together with `--extract' option (*note extracting files::). In this
5151 case, `tar' does not need to access snapshot file, since all the data
5152 necessary for extraction are stored in the archive itself. So, when
5153 extracting, you can give whatever argument to `--listed-incremental',
5154 the usual practice is to use `--listed-incremental=/dev/null'.
5155 Alternatively, you can use `--incremental', which needs no arguments.
5156 In general, `--incremental' (`-G') can be used as a shortcut for
5157 `--listed-incremental' when listing or extracting incremental backups
5158 (for more information regarding this option, *note incremental-op::).
5160 When extracting from the incremental backup GNU `tar' attempts to
5161 restore the exact state the file system had when the archive was
5162 created. In particular, it will _delete_ those files in the file
5163 system that did not exist in their directories when the archive was
5164 created. If you have created several levels of incremental files, then
5165 in order to restore the exact contents the file system had when the
5166 last level was created, you will need to restore from all backups in
5167 turn. Continuing our example, to restore the state of `/usr' file
5168 system, one would do(1):
5171 --listed-incremental=/dev/null \
5172 --file archive.1.tar
5174 --listed-incremental=/dev/null \
5175 --file archive.2.tar
5177 To list the contents of an incremental archive, use `--list' (*note
5178 list::), as usual. To obtain more information about the archive, use
5179 `--listed-incremental' or `--incremental' combined with two `--verbose'
5182 tar --list --incremental --verbose --verbose archive.tar
5184 This command will print, for each directory in the archive, the list
5185 of files in that directory at the time the archive was created. This
5186 information is put out in a format which is both human-readable and
5187 unambiguous for a program: each file name is printed as
5191 where X is a letter describing the status of the file: `Y' if the file
5192 is present in the archive, `N' if the file is not included in the
5193 archive, or a `D' if the file is a directory (and is included in the
5194 archive). *Note Dumpdir::, for the detailed description of dumpdirs
5195 and status codes. Each such line is terminated by a newline character.
5196 The last line is followed by an additional newline to indicate the end
5199 The option `--incremental' (`-G') gives the same behavior as
5200 `--listed-incremental' when used with `--list' and `--extract' options.
5201 When used with `--create' option, it creates an incremental archive
5202 without creating snapshot file. Thus, it is impossible to create
5203 several levels of incremental backups with `--incremental' option.
5205 ---------- Footnotes ----------
5207 (1) Notice, that since both archives were created without `-P'
5208 option (*note absolute::), these commands should be run from the root
5211 (2) Two `--verbose' options were selected to avoid breaking usual
5212 verbose listing output (`--list --verbose') when using in scripts.
5214 Versions of GNU `tar' up to 1.15.1 used to dump verbatim binary
5215 contents of the DUMPDIR header (with terminating nulls) when
5216 `--incremental' or `--listed-incremental' option was given, no matter
5217 what the verbosity level. This behavior, and, especially, the binary
5218 output it produced were considered inconvenient and were changed in
5222 File: tar.info, Node: Backup Levels, Next: Backup Parameters, Prev: Incremental Dumps, Up: Backups
5224 5.3 Levels of Backups
5225 =====================
5227 An archive containing all the files in the file system is called a
5228 "full backup" or "full dump". You could insure your data by creating a
5229 full dump every day. This strategy, however, would waste a substantial
5230 amount of archive media and user time, as unchanged files are daily
5233 It is more efficient to do a full dump only occasionally. To back up
5234 files between full dumps, you can use "incremental dumps". A "level
5235 one" dump archives all the files that have changed since the last full
5238 A typical dump strategy would be to perform a full dump once a week,
5239 and a level one dump once a day. This means some versions of files
5240 will in fact be archived more than once, but this dump strategy makes
5241 it possible to restore a file system to within one day of accuracy by
5242 only extracting two archives--the last weekly (full) dump and the last
5243 daily (level one) dump. The only information lost would be in files
5244 changed or created since the last daily backup. (Doing dumps more than
5245 once a day is usually not worth the trouble.)
5247 GNU `tar' comes with scripts you can use to do full and level-one
5248 (actually, even level-two and so on) dumps. Using scripts (shell
5249 programs) to perform backups and restoration is a convenient and
5250 reliable alternative to typing out file name lists and `tar' commands
5253 Before you use these scripts, you need to edit the file
5254 `backup-specs', which specifies parameters used by the backup scripts
5255 and by the restore script. This file is usually located in
5256 `/etc/backup' directory. *Note Backup Parameters::, for its detailed
5257 description. Once the backup parameters are set, you can perform
5258 backups or restoration by running the appropriate script.
5260 The name of the backup script is `backup'. The name of the restore
5261 script is `restore'. The following sections describe their use in
5264 _Please Note:_ The backup and restoration scripts are designed to be
5265 used together. While it is possible to restore files by hand from an
5266 archive which was created using a backup script, and to create an
5267 archive by hand which could then be extracted using the restore script,
5268 it is easier to use the scripts. *Note Incremental Dumps::, before
5269 making such an attempt.
5272 File: tar.info, Node: Backup Parameters, Next: Scripted Backups, Prev: Backup Levels, Up: Backups
5274 5.4 Setting Parameters for Backups and Restoration
5275 ==================================================
5277 The file `backup-specs' specifies backup parameters for the backup and
5278 restoration scripts provided with `tar'. You must edit `backup-specs'
5279 to fit your system configuration and schedule before using these
5282 Syntactically, `backup-specs' is a shell script, containing mainly
5283 variable assignments. However, any valid shell construct is allowed in
5284 this file. Particularly, you may wish to define functions within that
5285 script (e.g., see `RESTORE_BEGIN' below). For more information about
5286 shell script syntax, please refer to the definition of the Shell
5288 (http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
5289 g_02). See also *note Bash Features: (bashref)Top.
5291 The shell variables controlling behavior of `backup' and `restore'
5292 are described in the following subsections.
5296 * General-Purpose Variables::
5297 * Magnetic Tape Control::
5299 * backup-specs example:: An Example Text of `Backup-specs'
5302 File: tar.info, Node: General-Purpose Variables, Next: Magnetic Tape Control, Up: Backup Parameters
5304 5.4.1 General-Purpose Variables
5305 -------------------------------
5307 -- Backup variable: ADMINISTRATOR
5308 The user name of the backup administrator. `Backup' scripts sends
5309 a backup report to this address.
5311 -- Backup variable: BACKUP_HOUR
5312 The hour at which the backups are done. This can be a number from
5313 0 to 23, or the time specification in form HOURS:MINUTES, or the
5316 This variable is used by `backup'. Its value may be overridden
5317 using `--time' option (*note Scripted Backups::).
5319 -- Backup variable: TAPE_FILE
5320 The device `tar' writes the archive to. If TAPE_FILE is a remote
5321 archive (*note remote-dev::), backup script will suppose that your
5322 `mt' is able to access remote devices. If RSH (*note RSH::) is
5323 set, `--rsh-command' option will be added to invocations of `mt'.
5325 -- Backup variable: BLOCKING
5326 The blocking factor `tar' will use when writing the dump archive.
5327 *Note Blocking Factor::.
5329 -- Backup variable: BACKUP_DIRS
5330 A list of file systems to be dumped (for `backup'), or restored
5331 (for `restore'). You can include any directory name in the list
5332 -- subdirectories on that file system will be included, regardless
5333 of how they may look to other networked machines. Subdirectories
5334 on other file systems will be ignored.
5336 The host name specifies which host to run `tar' on, and should
5337 normally be the host that actually contains the file system.
5338 However, the host machine must have GNU `tar' installed, and must
5339 be able to access the directory containing the backup scripts and
5340 their support files using the same file name that is used on the
5341 machine where the scripts are run (i.e., what `pwd' will print
5342 when in that directory on that machine). If the host that contains
5343 the file system does not have this capability, you can specify
5344 another host as long as it can access the file system through NFS.
5346 If the list of file systems is very long you may wish to put it in
5347 a separate file. This file is usually named `/etc/backup/dirs',
5348 but this name may be overridden in `backup-specs' using `DIRLIST'
5351 -- Backup variable: DIRLIST
5352 The name of the file that contains a list of file systems to backup
5353 or restore. By default it is `/etc/backup/dirs'.
5355 -- Backup variable: BACKUP_FILES
5356 A list of individual files to be dumped (for `backup'), or restored
5357 (for `restore'). These should be accessible from the machine on
5358 which the backup script is run.
5360 If the list of individual files is very long you may wish to store
5361 it in a separate file. This file is usually named
5362 `/etc/backup/files', but this name may be overridden in
5363 `backup-specs' using `FILELIST' variable.
5365 -- Backup variable: FILELIST
5366 The name of the file that contains a list of individual files to
5367 backup or restore. By default it is `/etc/backup/files'.
5369 -- Backup variable: MT
5370 Full file name of `mt' binary.
5372 -- Backup variable: RSH
5373 Full file name of `rsh' binary or its equivalent. You may wish to
5374 set it to `ssh', to improve security. In this case you will have
5375 to use public key authentication.
5377 -- Backup variable: RSH_COMMAND
5378 Full file name of `rsh' binary on remote machines. This will be
5379 passed via `--rsh-command' option to the remote invocation of GNU
5382 -- Backup variable: VOLNO_FILE
5383 Name of temporary file to hold volume numbers. This needs to be
5384 accessible by all the machines which have file systems to be
5387 -- Backup variable: XLIST
5388 Name of "exclude file list". An "exclude file list" is a file
5389 located on the remote machine and containing the list of files to
5390 be excluded from the backup. Exclude file lists are searched in
5391 /etc/tar-backup directory. A common use for exclude file lists is
5392 to exclude files containing security-sensitive information (e.g.,
5393 `/etc/shadow' from backups).
5395 This variable affects only `backup'.
5397 -- Backup variable: SLEEP_TIME
5398 Time to sleep between dumps of any two successive file systems
5400 This variable affects only `backup'.
5402 -- Backup variable: DUMP_REMIND_SCRIPT
5403 Script to be run when it's time to insert a new tape in for the
5404 next volume. Administrators may want to tailor this script for
5405 their site. If this variable isn't set, GNU `tar' will display
5406 its built-in prompt, and will expect confirmation from the
5407 console. For the description of the default prompt, see *note
5408 change volume prompt::.
5411 -- Backup variable: SLEEP_MESSAGE
5412 Message to display on the terminal while waiting for dump time.
5413 Usually this will just be some literal text.
5415 -- Backup variable: TAR
5416 Full file name of the GNU `tar' executable. If this is not set,
5417 backup scripts will search `tar' in the current shell path.
5420 File: tar.info, Node: Magnetic Tape Control, Next: User Hooks, Prev: General-Purpose Variables, Up: Backup Parameters
5422 5.4.2 Magnetic Tape Control
5423 ---------------------------
5425 Backup scripts access tape device using special "hook functions".
5426 These functions take a single argument -- the name of the tape device.
5427 Their names are kept in the following variables:
5429 -- Backup variable: MT_BEGIN
5430 The name of "begin" function. This function is called before
5431 accessing the drive. By default it retensions the tape:
5436 mt -f "$1" retension
5439 -- Backup variable: MT_REWIND
5440 The name of "rewind" function. The default definition is as
5450 -- Backup variable: MT_OFFLINE
5451 The name of the function switching the tape off line. By default
5452 it is defined as follows:
5454 MT_OFFLINE=mt_offline
5460 -- Backup variable: MT_STATUS
5461 The name of the function used to obtain the status of the archive
5462 device, including error count. Default definition:
5471 File: tar.info, Node: User Hooks, Next: backup-specs example, Prev: Magnetic Tape Control, Up: Backup Parameters
5476 "User hooks" are shell functions executed before and after each `tar'
5477 invocation. Thus, there are "backup hooks", which are executed before
5478 and after dumping each file system, and "restore hooks", executed
5479 before and after restoring a file system. Each user hook is a shell
5480 function taking four arguments:
5482 -- User Hook Function: hook LEVEL HOST FS FSNAME
5486 Current backup or restore level.
5489 Name or IP address of the host machine being dumped or
5493 Full file name of the file system being dumped or restored.
5496 File system name with directory separators replaced with
5497 colons. This is useful, e.g., for creating unique files.
5499 Following variables keep the names of user hook functions:
5501 -- Backup variable: DUMP_BEGIN
5502 Dump begin function. It is executed before dumping the file
5505 -- Backup variable: DUMP_END
5506 Executed after dumping the file system.
5508 -- Backup variable: RESTORE_BEGIN
5509 Executed before restoring the file system.
5511 -- Backup variable: RESTORE_END
5512 Executed after restoring the file system.
5515 File: tar.info, Node: backup-specs example, Prev: User Hooks, Up: Backup Parameters
5517 5.4.4 An Example Text of `Backup-specs'
5518 ---------------------------------------
5520 The following is an example of `backup-specs':
5522 # site-specific parameters for file system backup.
5524 ADMINISTRATOR=friedman
5526 TAPE_FILE=/dev/nrsmt0
5528 # Use `ssh' instead of the less secure `rsh'
5530 RSH_COMMAND=/usr/bin/ssh
5532 # Override MT_STATUS function:
5538 # Disable MT_OFFLINE function
5555 apple-gunkies:/com/mailer/gnu
5556 apple-gunkies:/com/archive/gnu"
5558 BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
5561 File: tar.info, Node: Scripted Backups, Next: Scripted Restoration, Prev: Backup Parameters, Up: Backups
5563 5.5 Using the Backup Scripts
5564 ============================
5566 The syntax for running a backup script is:
5568 backup --level=LEVEL --time=TIME
5570 The `--level' option requests the dump level. Thus, to produce a
5571 full dump, specify `--level=0' (this is the default, so `--level' may
5572 be omitted if its value is `0')(1).
5574 The `--time' option determines when should the backup be run. TIME
5575 may take three forms:
5578 The dump must be run at HH hours MM minutes.
5581 The dump must be run at HH hours.
5584 The dump must be run immediately.
5586 You should start a script with a tape or disk mounted. Once you
5587 start a script, it prompts you for new tapes or disks as it needs them.
5588 Media volumes don't have to correspond to archive files -- a
5589 multi-volume archive can be started in the middle of a tape that
5590 already contains the end of another multi-volume archive. The
5591 `restore' script prompts for media by its archive volume, so to avoid
5592 an error message you should keep track of which tape (or disk) contains
5593 which volume of the archive (*note Scripted Restoration::).
5595 The backup scripts write two files on the file system. The first is
5596 a record file in `/etc/tar-backup/', which is used by the scripts to
5597 store and retrieve information about which files were dumped. This
5598 file is not meant to be read by humans, and should not be deleted by
5599 them. *Note Snapshot Files::, for a more detailed explanation of this
5602 The second file is a log file containing the names of the file
5603 systems and files dumped, what time the backup was made, and any error
5604 messages that were generated, as well as how much space was left in the
5605 media volume after the last volume of the archive was written. You
5606 should check this log file after every backup. The file name is
5607 `log-MM-DD-YYYY-level-N', where MM-DD-YYYY represents current date, and
5608 N represents current dump level number.
5610 The script also prints the name of each system being dumped to the
5613 Following is the full list of options accepted by `backup' script:
5617 Do backup level LEVEL (default 0).
5621 Force backup even if today's log file already exists.
5625 Set verbosity level. The higher the level is, the more debugging
5626 information will be output during execution. Default LEVEL is
5627 100, which means the highest debugging level.
5631 Wait till TIME, then do backup.
5635 Display short help message and exit.
5639 Display information about the program's name, version, origin and
5640 legal status, all on standard output, and then exit successfully.
5642 ---------- Footnotes ----------
5644 (1) For backward compatibility, the `backup' will also try to deduce
5645 the requested dump level from the name of the script itself. If the
5646 name consists of a string `level-' followed by a single decimal digit,
5647 that digit is taken as the dump level number. Thus, you may create a
5648 link from `backup' to `level-1' and then run `level-1' whenever you
5649 need to create a level one dump.
5652 File: tar.info, Node: Scripted Restoration, Prev: Scripted Backups, Up: Backups
5654 5.6 Using the Restore Script
5655 ============================
5657 To restore files that were archived using a scripted backup, use the
5658 `restore' script. Its usage is quite straightforward. In the simplest
5659 form, invoke `restore --all', it will then restore all the file systems
5660 and files specified in `backup-specs' (*note BACKUP_DIRS:
5661 General-Purpose Variables.).
5663 You may select the file systems (and/or files) to restore by giving
5664 `restore' a list of "patterns" in its command line. For example,
5669 will restore all file systems on the machine `albert'. A more
5670 complicated example:
5672 restore 'albert:*' '*:/var'
5674 This command will restore all file systems on the machine `albert' as
5675 well as `/var' file system on all machines.
5677 By default `restore' will start restoring files from the lowest
5678 available dump level (usually zero) and will continue through all
5679 available dump levels. There may be situations where such a thorough
5680 restore is not necessary. For example, you may wish to restore only
5681 files from the recent level one backup. To do so, use `--level'
5682 option, as shown in the example below:
5686 The full list of options accepted by `restore' follows:
5690 Restore all file systems and files specified in `backup-specs'.
5694 Start restoring from the given backup level, instead of the
5699 Set verbosity level. The higher the level is, the more debugging
5700 information will be output during execution. Default LEVEL is
5701 100, which means the highest debugging level.
5705 Display short help message and exit.
5709 Display information about the program's name, version, origin and
5710 legal status, all on standard output, and then exit successfully.
5712 You should start the restore script with the media containing the
5713 first volume of the archive mounted. The script will prompt for other
5714 volumes as they are needed. If the archive is on tape, you don't need
5715 to rewind the tape to to its beginning--if the tape head is positioned
5716 past the beginning of the archive, the script will rewind the tape as
5717 needed. *Note Tape Positioning::, for a discussion of tape positioning.
5719 *Warning:* The script will delete files from the active file
5720 system if they were not in the file system when the archive was
5723 *Note Incremental Dumps::, for an explanation of how the script makes
5727 File: tar.info, Node: Choosing, Next: Date input formats, Prev: Backups, Up: Top
5729 6 Choosing Files and Names for `tar'
5730 ************************************
5732 Certain options to `tar' enable you to specify a name for your archive.
5733 Other options let you decide which files to include or exclude from the
5734 archive, based on when or whether files were modified, whether the file
5735 names do or don't match specified patterns, or whether files are in
5736 specified directories.
5738 This chapter discusses these options in detail.
5742 * file:: Choosing the Archive's Name
5743 * Selecting Archive Members::
5744 * files:: Reading Names from a File
5745 * exclude:: Excluding Some Files
5746 * wildcards:: Wildcards Patterns and Matching
5747 * quoting styles:: Ways of Quoting Special Characters in Names
5748 * transform:: Modifying File and Member Names
5749 * after:: Operating Only on New Files
5750 * recurse:: Descending into Directories
5751 * one:: Crossing File System Boundaries
5754 File: tar.info, Node: file, Next: Selecting Archive Members, Up: Choosing
5756 6.1 Choosing and Naming Archive Files
5757 =====================================
5759 By default, `tar' uses an archive file name that was compiled when it
5760 was built on the system; usually this name refers to some physical tape
5761 drive on the machine. However, the person who installed `tar' on the
5762 system may not have set the default to a meaningful value as far as
5763 most users are concerned. As a result, you will usually want to tell
5764 `tar' where to find (or create) the archive. The `--file=ARCHIVE-NAME'
5765 (`-f ARCHIVE-NAME') option allows you to either specify or name a file
5766 to use as the archive instead of the default archive file location.
5768 `--file=ARCHIVE-NAME'
5770 Name the archive to create or operate on. Use in conjunction with
5773 For example, in this `tar' command,
5775 $ tar -cvf collection.tar blues folk jazz
5777 `collection.tar' is the name of the archive. It must directly follow
5778 the `-f' option, since whatever directly follows `-f' _will_ end up
5779 naming the archive. If you neglect to specify an archive name, you may
5780 end up overwriting a file in the working directory with the archive you
5781 create since `tar' will use this file's name for the archive name.
5783 An archive can be saved as a file in the file system, sent through a
5784 pipe or over a network, or written to an I/O device such as a tape,
5785 floppy disk, or CD write drive.
5787 If you do not name the archive, `tar' uses the value of the
5788 environment variable `TAPE' as the file name for the archive. If that
5789 is not available, `tar' uses a default, compiled-in archive name,
5790 usually that for tape unit zero (i.e., `/dev/tu00').
5792 If you use `-' as an ARCHIVE-NAME, `tar' reads the archive from
5793 standard input (when listing or extracting files), or writes it to
5794 standard output (when creating an archive). If you use `-' as an
5795 ARCHIVE-NAME when modifying an archive, `tar' reads the original
5796 archive from its standard input and writes the entire new archive to
5797 its standard output.
5799 The following example is a convenient way of copying directory
5800 hierarchy from `sourcedir' to `targetdir'.
5802 $ (cd sourcedir; tar -cf - .) | (cd targetdir; tar -xpf -)
5804 The `-C' option allows to avoid using subshells:
5806 $ tar -C sourcedir -cf - . | tar -C targetdir -xpf -
5808 In both examples above, the leftmost `tar' invocation archives the
5809 contents of `sourcedir' to the standard output, while the rightmost one
5810 reads this archive from its standard input and extracts it. The `-p'
5811 option tells it to restore permissions of the extracted files.
5813 To specify an archive file on a device attached to a remote machine,
5816 --file=HOSTNAME:/DEV/FILE-NAME
5818 `tar' will set up the remote connection, if possible, and prompt you
5819 for a username and password. If you use
5820 `--file=@HOSTNAME:/DEV/FILE-NAME', `tar' will attempt to set up the
5821 remote connection using your username as the username on the remote
5824 If the archive file name includes a colon (`:'), then it is assumed
5825 to be a file on another machine. If the archive file is
5826 `USER@HOST:FILE', then FILE is used on the host HOST. The remote host
5827 is accessed using the `rsh' program, with a username of USER. If the
5828 username is omitted (along with the `@' sign), then your user name will
5829 be used. (This is the normal `rsh' behavior.) It is necessary for the
5830 remote machine, in addition to permitting your `rsh' access, to have
5831 the `rmt' program installed (this command is included in the GNU `tar'
5832 distribution and by default is installed under `PREFIX/libexec/rmt',
5833 where PREFIX means your installation prefix). If you need to use a
5834 file whose name includes a colon, then the remote tape drive behavior
5835 can be inhibited by using the `--force-local' option.
5837 When the archive is being created to `/dev/null', GNU `tar' tries to
5838 minimize input and output operations. The Amanda backup system, when
5839 used with GNU `tar', has an initial sizing pass which uses this feature.
5842 File: tar.info, Node: Selecting Archive Members, Next: files, Prev: file, Up: Choosing
5844 6.2 Selecting Archive Members
5845 =============================
5847 "File Name arguments" specify which files in the file system `tar'
5848 operates on, when creating or adding to an archive, or which archive
5849 members `tar' operates on, when reading or deleting from an archive.
5852 To specify file names, you can include them as the last arguments on
5853 the command line, as follows:
5854 tar OPERATION [OPTION1 OPTION2 ...] [FILE NAME-1 FILE NAME-2 ...]
5856 If a file name begins with dash (`-'), precede it with `--add-file'
5857 option to prevent it from being treated as an option.
5859 By default GNU `tar' attempts to "unquote" each file or member name,
5860 replacing "escape sequences" according to the following table:
5862 Escape Replaced with
5863 -----------------------------------------------------------
5864 \a Audible bell (ASCII 7)
5865 \b Backspace (ASCII 8)
5866 \f Form feed (ASCII 12)
5867 \n New line (ASCII 10)
5868 \r Carriage return (ASCII 13)
5869 \t Horizontal tabulation (ASCII 9)
5870 \v Vertical tabulation (ASCII 11)
5872 \N ASCII N (N should be an octal number
5875 A backslash followed by any other symbol is retained.
5877 This default behavior is controlled by the following command line
5881 Enable unquoting input file or member names (default).
5884 Disable unquoting input file or member names.
5886 If you specify a directory name as a file name argument, all the
5887 files in that directory are operated on by `tar'.
5889 If you do not specify files, `tar' behavior differs depending on the
5890 operation mode as described below:
5892 When `tar' is invoked with `--create' (`-c'), `tar' will stop
5893 immediately, reporting the following:
5896 tar: Cowardly refusing to create an empty archive
5897 Try `tar --help' or `tar --usage' for more information.
5899 If you specify either `--list' (`-t') or `--extract' (`--get',
5900 `-x'), `tar' operates on all the archive members in the archive.
5902 If run with `--diff' option, tar will compare the archive with the
5903 contents of the current working directory.
5905 If you specify any other operation, `tar' does nothing.
5907 By default, `tar' takes file names from the command line. However,
5908 there are other ways to specify file or member names, or to modify the
5909 manner in which `tar' selects the files or members upon which to
5910 operate. In general, these methods work both for specifying the names
5911 of files and archive members.
5914 File: tar.info, Node: files, Next: exclude, Prev: Selecting Archive Members, Up: Choosing
5916 6.3 Reading Names from a File
5917 =============================
5919 Instead of giving the names of files or archive members on the command
5920 line, you can put the names into a file, and then use the
5921 `--files-from=FILE-OF-NAMES' (`-T FILE-OF-NAMES') option to `tar'.
5922 Give the name of the file which contains the list of files to include
5923 as the argument to `--files-from'. In the list, the file names should
5924 be separated by newlines. You will frequently use this option when you
5925 have generated the list of files to archive with the `find' utility.
5927 `--files-from=FILE-NAME'
5929 Get names to extract or create from file FILE-NAME.
5931 If you give a single dash as a file name for `--files-from', (i.e.,
5932 you specify either `--files-from=-' or `-T -'), then the file names are
5933 read from standard input.
5935 Unless you are running `tar' with `--create', you can not use both
5936 `--files-from=-' and `--file=-' (`-f -') in the same command.
5938 Any number of `-T' options can be given in the command line.
5940 The following example shows how to use `find' to generate a list of
5941 files smaller than 400K in length and put that list into a file called
5942 `small-files'. You can then use the `-T' option to `tar' to specify
5943 the files from that file, `small-files', to create the archive
5944 `little.tgz'. (The `-z' option to `tar' compresses the archive with
5945 `gzip'; *note gzip:: for more information.)
5947 $ find . -size -400 -print > small-files
5948 $ tar -c -v -z -T small-files -f little.tgz
5950 In the file list given by `-T' option, any file name beginning with `-'
5951 character is considered a `tar' option and is processed accordingly(1).
5952 For example, the common use of this feature is to change to another
5953 directory by specifying `-C' option:
5961 $ tar -c -f foo.tar --files-from list
5963 In this example, `tar' will first switch to `/etc' directory and add
5964 files `passwd' and `hosts' to the archive. Then it will change to
5965 `/lib' directory and will archive the file `libc.a'. Thus, the
5966 resulting archive `foo.tar' will contain:
5974 Notice that the option parsing algorithm used with `-T' is stricter
5975 than the one used by shell. Namely, when specifying option arguments,
5976 you should observe the following rules:
5978 * When using short (single-letter) option form, its argument must
5979 immediately follow the option letter, without any intervening
5980 whitespace. For example: `-Cdir'.
5982 * When using long option form, the option argument must be separated
5983 from the option by a single equal sign. No whitespace is allowed
5984 on any side of the equal sign. For example: `--directory=dir'.
5986 * For both short and long option forms, the option argument can be
5987 given on the next line after the option name, e.g.:
5997 If you happen to have a file whose name starts with `-', precede it
5998 with `--add-file' option to prevent it from being recognized as an
5999 option. For example: `--add-file=--my-file'.
6005 ---------- Footnotes ----------
6007 (1) Versions of GNU `tar' up to 1.15.1 recognized only `-C' option
6008 in file lists, and only if the option and its argument occupied two
6012 File: tar.info, Node: nul, Up: files
6014 6.3.1 `NUL'-Terminated File Names
6015 ---------------------------------
6017 The `--null' option causes `--files-from=FILE-OF-NAMES' (`-T
6018 FILE-OF-NAMES') to read file names terminated by a `NUL' instead of a
6019 newline, so files whose names contain newlines can be archived using
6023 Only consider `NUL'-terminated file names, instead of files that
6024 terminate in a newline.
6027 Undo the effect of any previous `--null' option.
6029 The `--null' option is just like the one in GNU `xargs' and `cpio',
6030 and is useful with the `-print0' predicate of GNU `find'. In `tar',
6031 `--null' also disables special handling for file names that begin with
6034 This example shows how to use `find' to generate a list of files
6035 larger than 800K in length and put that list into a file called
6036 `long-files'. The `-print0' option to `find' is just like `-print',
6037 except that it separates files with a `NUL' rather than with a newline.
6038 You can then run `tar' with both the `--null' and `-T' options to
6039 specify that `tar' gets the files from that file, `long-files', to
6040 create the archive `big.tgz'. The `--null' option to `tar' will cause
6041 `tar' to recognize the `NUL' separator between files.
6043 $ find . -size +800 -print0 > long-files
6044 $ tar -c -v --null --files-from=long-files --file=big.tar
6046 The `--no-null' option can be used if you need to read both
6047 `NUL'-terminated and newline-terminated files on the same command line.
6048 For example, if `flist' is a newline-terminated file, then the
6049 following command can be used to combine it with the above command:
6051 $ find . -size +800 -print0 |
6052 tar -c -f big.tar --null -T - --no-null -T flist
6054 This example uses short options for typographic reasons, to avoid
6057 GNU `tar' is able to automatically detect `NUL'-terminated file
6058 lists, so it is safe to use them even without the `--null' option. In
6059 this case `tar' will print a warning and continue reading such a file
6060 as if `--null' were actually given:
6062 $ find . -size +800 -print0 | tar -c -f big.tar -T -
6063 tar: -: file name read contains nul character
6065 The null terminator, however, remains in effect only for this
6066 particular file, any following `-T' options will assume newline
6067 termination. Of course, the null autodetection applies to these
6068 eventual surplus `-T' options as well.
6071 File: tar.info, Node: exclude, Next: wildcards, Prev: files, Up: Choosing
6073 6.4 Excluding Some Files
6074 ========================
6076 To avoid operating on files whose names match a particular pattern, use
6077 the `--exclude' or `--exclude-from' options.
6080 Causes `tar' to ignore files that match the PATTERN.
6082 The `--exclude=PATTERN' option prevents any file or member whose
6083 name matches the shell wildcard (PATTERN) from being operated on. For
6084 example, to create an archive with all the contents of the directory
6085 `src' except for files whose names end in `.o', use the command `tar
6086 -cf src.tar --exclude='*.o' src'.
6088 You may give multiple `--exclude' options.
6090 `--exclude-from=FILE'
6092 Causes `tar' to ignore files that match the patterns listed in
6095 Use the `--exclude-from' option to read a list of patterns, one per
6096 line, from FILE; `tar' will ignore files matching those patterns. Thus
6097 if `tar' is called as `tar -c -X foo .' and the file `foo' contains a
6098 single line `*.o', no files whose names end in `.o' will be added to
6101 Notice, that lines from FILE are read verbatim. One of the frequent
6102 errors is leaving some extra whitespace after a file name, which is
6103 difficult to catch using text editors.
6105 However, empty lines are OK.
6108 Exclude files and directories used by following version control
6109 systems: `CVS', `RCS', `SCCS', `SVN', `Arch', `Bazaar',
6110 `Mercurial', and `Darcs'.
6112 As of version 1.24, the following files are excluded:
6114 * `CVS/', and everything under it
6116 * `RCS/', and everything under it
6118 * `SCCS/', and everything under it
6120 * `.git/', and everything under it
6126 * `.svn/', and everything under it
6128 * `.arch-ids/', and everything under it
6130 * `{arch}/', and everything under it
6153 Exclude backup and lock files. This option causes exclusion of
6154 files that match the following shell globbing patterns:
6163 When creating an archive, the `--exclude-caches' option family
6164 causes `tar' to exclude all directories that contain a "cache directory
6165 tag". A cache directory tag is a short file with the well-known name
6166 `CACHEDIR.TAG' and having a standard header specified in
6167 `http://www.brynosaurus.com/cachedir/spec.html'. Various applications
6168 write cache directory tags into directories they use to hold
6169 regenerable, non-precious data, so that such data can be more easily
6170 excluded from backups.
6172 There are three `exclude-caches' options, each providing a different
6173 exclusion semantics:
6176 Do not archive the contents of the directory, but archive the
6177 directory itself and the `CACHEDIR.TAG' file.
6179 `--exclude-caches-under'
6180 Do not archive the contents of the directory, nor the
6181 `CACHEDIR.TAG' file, archive only the directory itself.
6183 `--exclude-caches-all'
6184 Omit directories containing `CACHEDIR.TAG' file entirely.
6186 Another option family, `--exclude-tag', provides a generalization of
6187 this concept. It takes a single argument, a file name to look for.
6188 Any directory that contains this file will be excluded from the dump.
6189 Similarly to `exclude-caches', there are three options in this option
6192 `--exclude-tag=FILE'
6193 Do not dump the contents of the directory, but dump the directory
6194 itself and the FILE.
6196 `--exclude-tag-under=FILE'
6197 Do not dump the contents of the directory, nor the FILE, archive
6198 only the directory itself.
6200 `--exclude-tag-all=FILE'
6201 Omit directories containing FILE file entirely.
6203 Multiple `--exclude-tag*' options can be given.
6205 For example, given this directory:
6216 The `--exclude-tag' will produce the following:
6218 $ tar -cf archive.tar --exclude-tag=tagfile -v dir
6223 tar: dir/folk/: contains a cache directory tag tagfile;
6227 Both the `dir/folk' directory and its tagfile are preserved in the
6228 archive, however the rest of files in this directory are not.
6230 Now, using the `--exclude-tag-under' option will exclude `tagfile'
6231 from the dump, while still preserving the directory itself, as shown in
6234 $ tar -cf archive.tar --exclude-tag-under=tagfile -v dir
6239 ./tar: dir/folk/: contains a cache directory tag tagfile;
6242 Finally, using `--exclude-tag-all' omits the `dir/folk' directory
6245 $ tar -cf archive.tar --exclude-tag-all=tagfile -v dir
6249 ./tar: dir/folk/: contains a cache directory tag tagfile;
6250 directory not dumped
6254 * problems with exclude::
6257 File: tar.info, Node: problems with exclude, Up: exclude
6259 Problems with Using the `exclude' Options
6260 -----------------------------------------
6262 Some users find `exclude' options confusing. Here are some common
6265 * The main operating mode of `tar' does not act on a file name
6266 explicitly listed on the command line, if one of its file name
6267 components is excluded. In the example above, if you create an
6268 archive and exclude files that end with `*.o', but explicitly name
6269 the file `dir.o/foo' after all the options have been listed,
6270 `dir.o/foo' will be excluded from the archive.
6272 * You can sometimes confuse the meanings of `--exclude' and
6273 `--exclude-from'. Be careful: use `--exclude' when files to be
6274 excluded are given as a pattern on the command line. Use
6275 `--exclude-from' to introduce the name of a file which contains a
6276 list of patterns, one per line; each of these patterns can exclude
6277 zero, one, or many files.
6279 * When you use `--exclude=PATTERN', be sure to quote the PATTERN
6280 parameter, so GNU `tar' sees wildcard characters like `*'. If you
6281 do not do this, the shell might expand the `*' itself using files
6282 at hand, so `tar' might receive a list of files instead of one
6283 pattern, or none at all, making the command somewhat illegal.
6284 This might not correspond to what you want.
6288 $ tar -c -f ARCHIVE.TAR --exclude '*.o' DIRECTORY
6293 $ tar -c -f ARCHIVE.TAR --exclude *.o DIRECTORY
6295 * You must use use shell syntax, or globbing, rather than `regexp'
6296 syntax, when using exclude options in `tar'. If you try to use
6297 `regexp' syntax to describe files to be excluded, your command
6300 * In earlier versions of `tar', what is now the `--exclude-from'
6301 option was called `--exclude' instead. Now, `--exclude' applies
6302 to patterns listed on the command line and `--exclude-from'
6303 applies to patterns listed in a file.
6307 File: tar.info, Node: wildcards, Next: quoting styles, Prev: exclude, Up: Choosing
6309 6.5 Wildcards Patterns and Matching
6310 ===================================
6312 "Globbing" is the operation by which "wildcard" characters, `*' or `?'
6313 for example, are replaced and expanded into all existing files matching
6314 the given pattern. GNU `tar' can use wildcard patterns for matching
6315 (or globbing) archive members when extracting from or listing an
6316 archive. Wildcard patterns are also used for verifying volume labels
6317 of `tar' archives. This section has the purpose of explaining wildcard
6320 A PATTERN should be written according to shell syntax, using wildcard
6321 characters to effect globbing. Most characters in the pattern stand
6322 for themselves in the matched string, and case is significant: `a' will
6323 match only `a', and not `A'. The character `?' in the pattern matches
6324 any single character in the matched string. The character `*' in the
6325 pattern matches zero, one, or more single characters in the matched
6326 string. The character `\' says to take the following character of the
6327 pattern _literally_; it is useful when one needs to match the `?', `*',
6328 `[' or `\' characters, themselves.
6330 The character `[', up to the matching `]', introduces a character
6331 class. A "character class" is a list of acceptable characters for the
6332 next single character of the matched string. For example, `[abcde]'
6333 would match any of the first five letters of the alphabet. Note that
6334 within a character class, all of the "special characters" listed above
6335 other than `\' lose their special meaning; for example, `[-\\[*?]]'
6336 would match any of the characters, `-', `\', `[', `*', `?', or `]'.
6337 (Due to parsing constraints, the characters `-' and `]' must either
6338 come _first_ or _last_ in a character class.)
6340 If the first character of the class after the opening `[' is `!' or
6341 `^', then the meaning of the class is reversed. Rather than listing
6342 character to match, it lists those characters which are _forbidden_ as
6343 the next single character of the matched string.
6345 Other characters of the class stand for themselves. The special
6346 construction `[A-E]', using an hyphen between two letters, is meant to
6347 represent all characters between A and E, inclusive.
6349 Periods (`.') or forward slashes (`/') are not considered special
6350 for wildcard matches. However, if a pattern completely matches a
6351 directory prefix of a matched string, then it matches the full matched
6352 string: thus, excluding a directory also excludes all the files beneath
6357 * controlling pattern-matching::
6360 File: tar.info, Node: controlling pattern-matching, Up: wildcards
6362 Controlling Pattern-Matching
6363 ----------------------------
6365 For the purposes of this section, we call "exclusion members" all
6366 member names obtained while processing `--exclude' and `--exclude-from'
6367 options, and "inclusion members" those member names that were given in
6368 the command line or read from the file specified with `--files-from'
6371 These two pairs of member lists are used in the following operations:
6372 `--diff', `--extract', `--list', `--update'.
6374 There are no inclusion members in create mode (`--create' and
6375 `--append'), since in this mode the names obtained from the command
6376 line refer to _files_, not archive members.
6378 By default, inclusion members are compared with archive members
6379 literally (1) and exclusion members are treated as globbing patterns.
6387 # Member names are used verbatim:
6388 $ tar -xf foo.tar -v '[remarks]'
6390 # Exclude member names are globbed:
6391 $ tar -xf foo.tar -v --exclude '*.c'
6395 This behavior can be altered by using the following options:
6398 Treat all member names as wildcards.
6401 Treat all member names as literal strings.
6403 Thus, to extract files whose names end in `.c', you can use:
6405 $ tar -xf foo.tar -v --wildcards '*.c'
6409 Notice quoting of the pattern to prevent the shell from interpreting it.
6411 The effect of `--wildcards' option is canceled by `--no-wildcards'.
6412 This can be used to pass part of the command line arguments verbatim
6413 and other part as globbing patterns. For example, the following
6416 $ tar -xf foo.tar --wildcards '*.txt' --no-wildcards '[remarks]'
6418 instructs `tar' to extract from `foo.tar' all files whose names end in
6419 `.txt' and the file named `[remarks]'.
6421 Normally, a pattern matches a name if an initial subsequence of the
6422 name's components matches the pattern, where `*', `?', and `[...]' are
6423 the usual shell wildcards, `\' escapes wildcards, and wildcards can
6426 Other than optionally stripping leading `/' from names (*note
6427 absolute::), patterns and names are used as-is. For example, trailing
6428 `/' is not trimmed from a user-specified name before deciding whether
6431 However, this matching procedure can be altered by the options listed
6432 below. These options accumulate. For example:
6434 --ignore-case --exclude='makefile' --no-ignore-case ---exclude='readme'
6436 ignores case when excluding `makefile', but not when excluding `readme'.
6440 If anchored, a pattern must match an initial subsequence of the
6441 name's components. Otherwise, the pattern can match any
6442 subsequence. Default is `--no-anchored' for exclusion members and
6443 `--anchored' inclusion members.
6447 When ignoring case, upper-case patterns match lower-case names and
6448 vice versa. When not ignoring case (the default), matching is
6451 `--wildcards-match-slash'
6452 `--no-wildcards-match-slash'
6453 When wildcards match slash (the default for exclusion members), a
6454 wildcard like `*' in the pattern can match a `/' in the name.
6455 Otherwise, `/' is matched only by `/'.
6458 The `--recursion' and `--no-recursion' options (*note recurse::)
6459 also affect how member patterns are interpreted. If recursion is in
6460 effect, a pattern matches a name if it matches any of the name's parent
6463 The following table summarizes pattern-matching default values:
6465 Members Default settings
6466 --------------------------------------------------------------------------
6467 Inclusion `--no-wildcards --anchored
6468 --no-wildcards-match-slash'
6469 Exclusion `--wildcards --no-anchored
6470 --wildcards-match-slash'
6472 ---------- Footnotes ----------
6474 (1) Notice that earlier GNU `tar' versions used globbing for
6475 inclusion members, which contradicted to UNIX98 specification and was
6476 not documented. *Note Changes::, for more information on this and other
6480 File: tar.info, Node: quoting styles, Next: transform, Prev: wildcards, Up: Choosing
6482 6.6 Quoting Member Names
6483 ========================
6485 When displaying member names, `tar' takes care to avoid ambiguities
6486 caused by certain characters. This is called "name quoting". The
6487 characters in question are:
6489 * Non-printable control characters:
6490 Character ASCII Character name
6491 ---------------------------------------------------------------
6496 \r 13 Carriage return
6497 \t 9 Horizontal tabulation
6498 \v 11 Vertical tabulation
6502 * Single and double quotes (`'' and `"')
6506 The exact way `tar' uses to quote these characters depends on the
6507 "quoting style". The default quoting style, called "escape" (see
6508 below), uses backslash notation to represent control characters, space
6509 and backslash. Using this quoting style, control characters are
6510 represented as listed in column `Character' in the above table, a space
6511 is printed as `\ ' and a backslash as `\\'.
6513 GNU `tar' offers seven distinct quoting styles, which can be selected
6514 using `--quoting-style' option:
6516 `--quoting-style=STYLE'
6517 Sets quoting style. Valid values for STYLE argument are: literal,
6518 shell, shell-always, c, escape, locale, clocale.
6520 These styles are described in detail below. To illustrate their
6521 effect, we will use an imaginary tar archive `arch.tar' containing the
6524 # 1. Contains horizontal tabulation character.
6526 # 2. Contains newline character
6529 # 3. Contains a space
6531 # 4. Contains double quotes
6533 # 5. Contains single quotes
6535 # 6. Contains a backslash character:
6538 Here is how usual `ls' command would have listed them, if they had
6539 existed in the current working directory:
6552 No quoting, display each character as is:
6554 $ tar tf arch.tar --quoting-style=literal
6565 Display characters the same way Bourne shell does: control
6566 characters, except `\t' and `\n', are printed using backslash
6567 escapes, `\t' and `\n' are printed as is, and a single quote is
6568 printed as `\''. If a name contains any quoted characters, it is
6569 enclosed in single quotes. In particular, if a name contains
6570 single quotes, it is printed as several single-quoted strings:
6572 $ tar tf arch.tar --quoting-style=shell
6575 './a'\''single'\''quote'
6583 Same as `shell', but the names are always enclosed in single
6586 $ tar tf arch.tar --quoting-style=shell-always
6589 './a'\''single'\''quote'
6597 Use the notation of the C programming language. All names are
6598 enclosed in double quotes. Control characters are quoted using
6599 backslash notations, double quotes are represented as `\"',
6600 backslash characters are represented as `\\'. Single quotes and
6601 spaces are not quoted:
6603 $ tar tf arch.tar --quoting-style=c
6607 "./a\"double\"quote"
6613 Control characters are printed using backslash notation, a space is
6614 printed as `\ ' and a backslash as `\\'. This is the default
6615 quoting style, unless it was changed when configured the package.
6617 $ tar tf arch.tar --quoting-style=escape
6627 Control characters, single quote and backslash are printed using
6628 backslash notation. All names are quoted using left and right
6629 quotation marks, appropriate to the current locale. If it does not
6630 define quotation marks, use ``' as left and `'' as right quotation
6631 marks. Any occurrences of the right quotation mark in a name are
6632 escaped with `\', for example:
6636 $ tar tf arch.tar --quoting-style=locale
6639 `./a\'single\'quote'
6646 Same as `locale', but `"' is used for both left and right
6647 quotation marks, if not provided by the currently selected locale:
6649 $ tar tf arch.tar --quoting-style=clocale
6653 "./a\"double\"quote"
6658 You can specify which characters should be quoted in addition to
6659 those implied by the current quoting style:
6661 `--quote-chars=STRING'
6662 Always quote characters from STRING, even if the selected quoting
6663 style would not quote them.
6665 For example, using `escape' quoting (compare with the usual escape
6668 $ tar tf arch.tar --quoting-style=escape --quote-chars=' "'
6677 To disable quoting of such additional characters, use the following
6680 `--no-quote-chars=STRING'
6681 Remove characters listed in STRING from the list of quoted
6682 characters set by the previous `--quote-chars' option.
6684 This option is particularly useful if you have added `--quote-chars'
6685 to your `TAR_OPTIONS' (*note TAR_OPTIONS::) and wish to disable it for
6686 the current invocation.
6688 Note, that `--no-quote-chars' does _not_ disable those characters
6689 that are quoted by default in the selected quoting style.
6692 File: tar.info, Node: transform, Next: after, Prev: quoting styles, Up: Choosing
6694 6.7 Modifying File and Member Names
6695 ===================================
6697 `Tar' archives contain detailed information about files stored in them
6698 and full file names are part of that information. When storing a file
6699 to an archive, its file name is recorded in it, along with the actual
6700 file contents. When restoring from an archive, a file is created on
6701 disk with exactly the same name as that stored in the archive. In the
6702 majority of cases this is the desired behavior of a file archiver.
6703 However, there are some cases when it is not.
6705 First of all, it is often unsafe to extract archive members with
6706 absolute file names or those that begin with a `../'. GNU `tar' takes
6707 special precautions when extracting such names and provides a special
6708 option for handling them, which is described in *note absolute::.
6710 Secondly, you may wish to extract file names without some leading
6711 directory components, or with otherwise modified names. In other cases
6712 it is desirable to store files under differing names in the archive.
6714 GNU `tar' provides several options for these needs.
6716 `--strip-components=NUMBER'
6717 Strip given NUMBER of leading components from file names before
6720 For example, suppose you have archived whole `/usr' hierarchy to a
6721 tar archive named `usr.tar'. Among other files, this archive contains
6722 `usr/include/stdlib.h', which you wish to extract to the current
6723 working directory. To do so, you type:
6725 $ tar -xf usr.tar --strip=2 usr/include/stdlib.h
6727 The option `--strip=2' instructs `tar' to strip the two leading
6728 components (`usr/' and `include/') off the file name.
6730 If you add the `--verbose' (`-v') option to the invocation above,
6731 you will note that the verbose listing still contains the full file
6732 name, with the two removed components still in place. This can be
6733 inconvenient, so `tar' provides a special option for altering this
6736 `--show-transformed-names'
6737 Display file or member names with all requested transformations
6742 $ tar -xf usr.tar -v --strip=2 usr/include/stdlib.h
6743 usr/include/stdlib.h
6744 $ tar -xf usr.tar -v --strip=2 --show-transformed usr/include/stdlib.h
6747 Notice that in both cases the file `stdlib.h' is extracted to the
6748 current working directory, `--show-transformed-names' affects only the
6749 way its name is displayed.
6751 This option is especially useful for verifying whether the invocation
6752 will have the desired effect. Thus, before running
6756 it is often advisable to run
6758 $ tar -t -v --show-transformed --strip=N
6760 to make sure the command will produce the intended results.
6762 In case you need to apply more complex modifications to the file
6763 name, GNU `tar' provides a general-purpose transformation option:
6765 `--transform=EXPRESSION'
6766 `--xform=EXPRESSION'
6767 Modify file names using supplied EXPRESSION.
6769 The EXPRESSION is a `sed'-like replace expression of the form:
6771 s/REGEXP/REPLACE/[FLAGS]
6773 where REGEXP is a "regular expression", REPLACE is a replacement for
6774 each file name part that matches REGEXP. Both REGEXP and REPLACE are
6775 described in detail in *note The "s" Command: (sed)The "s" Command.
6777 Any delimiter can be used in lieu of `/', the only requirement being
6778 that it be used consistently throughout the expression. For example,
6779 the following two expressions are equivalent:
6784 Changing delimiters is often useful when the REGEX contains slashes.
6785 For example, it is more convenient to write `s,/,-,' than `s/\//-/'.
6787 As in `sed', you can give several replace expressions, separated by
6790 Supported FLAGS are:
6793 Apply the replacement to _all_ matches to the REGEXP, not just the
6797 Use case-insensitive matching.
6800 REGEXP is an "extended regular expression" (*note Extended regular
6801 expressions: (sed)Extended regexps.).
6804 Only replace the NUMBERth match of the REGEXP.
6806 Note: the POSIX standard does not specify what should happen when
6807 you mix the `g' and NUMBER modifiers. GNU `tar' follows the GNU
6808 `sed' implementation in this regard, so the interaction is defined
6809 to be: ignore matches before the NUMBERth, and then match and
6810 replace all matches from the NUMBERth on.
6813 In addition, several "transformation scope" flags are supported,
6814 that control to what files transformations apply. These are:
6817 Apply transformation to regular archive members.
6820 Do not apply transformation to regular archive members.
6823 Apply transformation to symbolic link targets.
6826 Do not apply transformation to symbolic link targets.
6829 Apply transformation to hard link targets.
6832 Do not apply transformation to hard link targets.
6834 Default is `rsh', which means to apply tranformations to both archive
6835 members and targets of symbolic and hard links.
6837 Default scope flags can also be changed using `flags=' statement in
6838 the transform expression. The flags set this way remain in force until
6839 next `flags=' statement or end of expression, whichever occurs first.
6842 --transform 'flags=S;s|^|/usr/local/|'
6844 Here are several examples of `--transform' usage:
6846 1. Extract `usr/' hierarchy into `usr/local/':
6848 $ tar --transform='s,usr/,usr/local/,' -x -f arch.tar
6850 2. Strip two leading directory components (equivalent to
6851 `--strip-components=2'):
6853 $ tar --transform='s,/*[^/]*/[^/]*/,,' -x -f arch.tar
6855 3. Convert each file name to lower case:
6857 $ tar --transform 's/.*/\L&/' -x -f arch.tar
6859 4. Prepend `/prefix/' to each file name:
6861 $ tar --transform 's,^,/prefix/,' -x -f arch.tar
6863 5. Archive the `/lib' directory, prepending `/usr/local' to each
6866 $ tar --transform 's,^,/usr/local/,S' -c -f arch.tar /lib
6868 Notice the use of flags in the last example. The `/lib' directory
6869 often contains many symbolic links to files within it. It may look,
6870 for example, like this:
6873 drwxr-xr-x root/root 0 2008-07-08 16:20 /lib/
6874 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /lib/libc-2.3.2.so
6875 lrwxrwxrwx root/root 0 2008-06-24 17:12 /lib/libc.so.6 -> libc-2.3.2.so
6878 Using the expression `s,^,/usr/local/,' would mean adding
6879 `/usr/local' to both regular archive members and to link targets. In
6880 this case, `/lib/libc.so.6' would become:
6882 /usr/local/lib/libc.so.6 -> /usr/local/libc-2.3.2.so
6884 This is definitely not desired. To avoid this, the `S' flag is
6885 used, which excludes symbolic link targets from filename
6886 transformations. The result is:
6888 $ tar --transform 's,^,/usr/local/,S', -c -v -f arch.tar \
6889 --show-transformed /lib
6890 drwxr-xr-x root/root 0 2008-07-08 16:20 /usr/local/lib/
6891 -rwxr-xr-x root/root 1250840 2008-05-25 07:44 /usr/local/lib/libc-2.3.2.so
6892 lrwxrwxrwx root/root 0 2008-06-24 17:12 /usr/local/lib/libc.so.6 \
6895 Unlike `--strip-components', `--transform' can be used in any GNU
6896 `tar' operation mode. For example, the following command adds files to
6897 the archive while replacing the leading `usr/' component with `var/':
6899 $ tar -cf arch.tar --transform='s,^usr/,var/,' /
6901 To test `--transform' effect we suggest using
6902 `--show-transformed-names' option:
6904 $ tar -cf arch.tar --transform='s,^usr/,var/,' \
6905 --verbose --show-transformed-names /
6907 If both `--strip-components' and `--transform' are used together,
6908 then `--transform' is applied first, and the required number of
6909 components is then stripped from its result.
6911 You can use as many `--transform' options in a single command line
6912 as you want. The specified expressions will then be applied in order
6913 of their appearance. For example, the following two invocations are
6916 $ tar -cf arch.tar --transform='s,/usr/var,/var/' \
6917 --transform='s,/usr/local,/usr/,'
6918 $ tar -cf arch.tar \
6919 --transform='s,/usr/var,/var/;s,/usr/local,/usr/,'
6922 File: tar.info, Node: after, Next: recurse, Prev: transform, Up: Choosing
6924 6.8 Operating Only on New Files
6925 ===============================
6927 The `--after-date=DATE' (`--newer=DATE', `-N DATE') option causes `tar'
6928 to only work on files whose data modification or status change times
6929 are newer than the DATE given. If DATE starts with `/' or `.', it is
6930 taken to be a file name; the data modification time of that file is
6931 used as the date. If you use this option when creating or appending to
6932 an archive, the archive will only include new files. If you use
6933 `--after-date' when extracting an archive, `tar' will only extract
6934 files newer than the DATE you specify.
6936 If you only want `tar' to make the date comparison based on
6937 modification of the file's data (rather than status changes), then use
6938 the `--newer-mtime=DATE' option.
6940 You may use these options with any operation. Note that these
6941 options differ from the `--update' (`-u') operation in that they allow
6942 you to specify a particular date against which `tar' can compare when
6943 deciding whether or not to archive the files.
6948 Only store files newer than DATE.
6950 Acts on files only if their data modification or status change
6951 times are later than DATE. Use in conjunction with any operation.
6953 If DATE starts with `/' or `.', it is taken to be a file name; the
6954 data modification time of that file is used as the date.
6956 `--newer-mtime=DATE'
6957 Acts like `--after-date', but only looks at data modification
6960 These options limit `tar' to operate only on files which have been
6961 modified after the date specified. A file's status is considered to
6962 have changed if its contents have been modified, or if its owner,
6963 permissions, and so forth, have been changed. (For more information on
6964 how to specify a date, see *note Date input formats::; remember that the
6965 entire date argument must be quoted if it contains any spaces.)
6967 Gurus would say that `--after-date' tests both the data modification
6968 time (`mtime', the time the contents of the file were last modified)
6969 and the status change time (`ctime', the time the file's status was
6970 last changed: owner, permissions, etc.) fields, while `--newer-mtime'
6971 tests only the `mtime' field.
6973 To be precise, `--after-date' checks _both_ `mtime' and `ctime' and
6974 processes the file if either one is more recent than DATE, while
6975 `--newer-mtime' only checks `mtime' and disregards `ctime'. Neither
6976 does it use `atime' (the last time the contents of the file were looked
6979 Date specifiers can have embedded spaces. Because of this, you may
6980 need to quote date arguments to keep the shell from parsing them as
6981 separate arguments. For example, the following command will add to the
6982 archive all the files modified less than two days ago:
6984 $ tar -cf foo.tar --newer-mtime '2 days ago'
6986 When any of these options is used with the option `--verbose' (*note
6987 verbose tutorial::) GNU `tar' will try to convert the specified date
6988 back to its textual representation and compare that with the one given
6989 with the option. If the two dates differ, `tar' will print a warning
6990 saying what date it will use. This is to help user ensure he is using
6991 the right date. For example:
6993 $ tar -c -f archive.tar --after-date='10 days ago' .
6994 tar: Option --after-date: Treating date `10 days ago' as 2006-06-11
6997 *Please Note:* `--after-date' and `--newer-mtime' should not be
6998 used for incremental backups. *Note Incremental Dumps::, for
6999 proper way of creating incremental backups.
7002 File: tar.info, Node: recurse, Next: one, Prev: after, Up: Choosing
7004 6.9 Descending into Directories
7005 ===============================
7007 Usually, `tar' will recursively explore all directories (either those
7008 given on the command line or through the `--files-from' option) for the
7009 various files they contain. However, you may not always want `tar' to
7012 The `--no-recursion' option inhibits `tar''s recursive descent into
7013 specified directories. If you specify `--no-recursion', you can use
7014 the `find' (*note find: (find)Top.) utility for hunting through levels
7015 of directories to construct a list of file names which you could then
7016 pass to `tar'. `find' allows you to be more selective when choosing
7017 which files to archive; see *note files::, for more information on
7018 using `find' with `tar'.
7021 Prevents `tar' from recursively descending directories.
7024 Requires `tar' to recursively descend directories. This is the
7027 When you use `--no-recursion', GNU `tar' grabs directory entries
7028 themselves, but does not descend on them recursively. Many people use
7029 `find' for locating files they want to back up, and since `tar'
7030 _usually_ recursively descends on directories, they have to use the
7031 `-not -type d' test in their `find' invocation (*note Type:
7032 (find)Type.), as they usually do not want all the files in a directory.
7033 They then use the `--files-from' option to archive the files located
7036 The problem when restoring files archived in this manner is that the
7037 directories themselves are not in the archive; so the
7038 `--same-permissions' (`--preserve-permissions', `-p') option does not
7039 affect them--while users might really like it to. Specifying
7040 `--no-recursion' is a way to tell `tar' to grab only the directory
7041 entries given to it, adding no new files on its own. To summarize, if
7042 you use `find' to create a list of files to be stored in an archive,
7045 $ find DIR TESTS | \
7046 tar -cf ARCHIVE -T - --no-recursion
7048 The `--no-recursion' option also applies when extracting: it causes
7049 `tar' to extract only the matched directory entries, not the files
7050 under those directories.
7052 The `--no-recursion' option also affects how globbing patterns are
7053 interpreted (*note controlling pattern-matching::).
7055 The `--no-recursion' and `--recursion' options apply to later
7056 options and operands, and can be overridden by later occurrences of
7057 `--no-recursion' and `--recursion'. For example:
7059 $ tar -cf jams.tar --no-recursion grape --recursion grape/concord
7061 creates an archive with one entry for `grape', and the recursive
7062 contents of `grape/concord', but no entries under `grape' other than
7066 File: tar.info, Node: one, Prev: recurse, Up: Choosing
7068 6.10 Crossing File System Boundaries
7069 ====================================
7071 `tar' will normally automatically cross file system boundaries in order
7072 to archive files which are part of a directory tree. You can change
7073 this behavior by running `tar' and specifying `--one-file-system'.
7074 This option only affects files that are archived because they are in a
7075 directory that is being archived; `tar' will still archive files
7076 explicitly named on the command line or through `--files-from',
7077 regardless of where they reside.
7080 Prevents `tar' from crossing file system boundaries when
7081 archiving. Use in conjunction with any write operation.
7083 The `--one-file-system' option causes `tar' to modify its normal
7084 behavior in archiving the contents of directories. If a file in a
7085 directory is not on the same file system as the directory itself, then
7086 `tar' will not archive that file. If the file is a directory itself,
7087 `tar' will not archive anything beneath it; in other words, `tar' will
7088 not cross mount points.
7090 This option is useful for making full or incremental archival
7091 backups of a file system. If this option is used in conjunction with
7092 `--verbose' (`-v'), files that are excluded are mentioned by name on
7097 * directory:: Changing Directory
7098 * absolute:: Absolute File Names
7101 File: tar.info, Node: directory, Next: absolute, Up: one
7103 6.10.1 Changing the Working Directory
7104 -------------------------------------
7106 To change the working directory in the middle of a list of file names,
7107 either on the command line or in a file specified using `--files-from'
7108 (`-T'), use `--directory' (`-C'). This will change the working
7109 directory to the specified directory after that point in the list.
7111 `--directory=DIRECTORY'
7113 Changes the working directory in the middle of a command line.
7117 $ tar -c -f jams.tar grape prune -C food cherry
7119 will place the files `grape' and `prune' from the current directory
7120 into the archive `jams.tar', followed by the file `cherry' from the
7121 directory `food'. This option is especially useful when you have
7122 several widely separated files that you want to store in the same
7125 Note that the file `cherry' is recorded in the archive under the
7126 precise name `cherry', _not_ `food/cherry'. Thus, the archive will
7127 contain three files that all appear to have come from the same
7128 directory; if the archive is extracted with plain `tar --extract', all
7129 three files will be written in the current directory.
7131 Contrast this with the command,
7133 $ tar -c -f jams.tar grape prune -C food red/cherry
7135 which records the third file in the archive under the name `red/cherry'
7136 so that, if the archive is extracted using `tar --extract', the third
7137 file will be written in a subdirectory named `red'.
7139 You can use the `--directory' option to make the archive independent
7140 of the original name of the directory holding the files. The following
7141 command places the files `/etc/passwd', `/etc/hosts', and `/lib/libc.a'
7142 into the archive `foo.tar':
7144 $ tar -c -f foo.tar -C /etc passwd hosts -C /lib libc.a
7146 However, the names of the archive members will be exactly what they were
7147 on the command line: `passwd', `hosts', and `libc.a'. They will not
7148 appear to be related by file name to the original directories where
7149 those files were located.
7151 Note that `--directory' options are interpreted consecutively. If
7152 `--directory' specifies a relative file name, it is interpreted
7153 relative to the then current directory, which might not be the same as
7154 the original current working directory of `tar', due to a previous
7155 `--directory' option.
7157 When using `--files-from' (*note files::), you can put various `tar'
7158 options (including `-C') in the file list. Notice, however, that in
7159 this case the option and its argument may not be separated by
7160 whitespace. If you use short option, its argument must either follow
7161 the option letter immediately, without any intervening whitespace, or
7162 occupy the next line. Otherwise, if you use long option, separate its
7163 argument by an equal sign.
7165 For instance, the file list for the above example will be:
7173 To use it, you would invoke `tar' as follows:
7175 $ tar -c -f foo.tar --files-from list
7177 The interpretation of `--directory' is disabled by `--null' option.
7180 File: tar.info, Node: absolute, Prev: directory, Up: one
7182 6.10.2 Absolute File Names
7183 --------------------------
7185 By default, GNU `tar' drops a leading `/' on input or output, and
7186 complains about file names containing a `..' component. There is an
7187 option that turns off this behavior:
7191 Do not strip leading slashes from file names, and permit file names
7192 containing a `..' file name component.
7194 When `tar' extracts archive members from an archive, it strips any
7195 leading slashes (`/') from the member name. This causes absolute
7196 member names in the archive to be treated as relative file names. This
7197 allows you to have such members extracted wherever you want, instead of
7198 being restricted to extracting the member in the exact directory named
7199 in the archive. For example, if the archive member has the name
7200 `/etc/passwd', `tar' will extract it as if the name were really
7203 File names containing `..' can cause problems when extracting, so
7204 `tar' normally warns you about such files when creating an archive, and
7205 rejects attempts to extracts such files.
7207 Other `tar' programs do not do this. As a result, if you create an
7208 archive whose member names start with a slash, they will be difficult
7209 for other people with a non-GNU `tar' program to use. Therefore, GNU
7210 `tar' also strips leading slashes from member names when putting
7211 members into the archive. For example, if you ask `tar' to add the file
7212 `/bin/ls' to an archive, it will do so, but the member name will be
7215 If you use the `--absolute-names' (`-P') option, `tar' will do none
7216 of these transformations.
7218 To archive or extract files relative to the root directory, specify
7219 the `--absolute-names' (`-P') option.
7221 Normally, `tar' acts on files relative to the working
7222 directory--ignoring superior directory names when archiving, and
7223 ignoring leading slashes when extracting.
7225 When you specify `--absolute-names' (`-P'), `tar' stores file names
7226 including all superior directory names, and preserves leading slashes.
7227 If you only invoked `tar' from the root directory you would never need
7228 the `--absolute-names' option, but using this option may be more
7229 convenient than switching to root.
7232 Preserves full file names (including superior directory names) when
7233 archiving files. Preserves leading slash when extracting files.
7236 `tar' prints out a message about removing the `/' from file names.
7237 This message appears once per GNU `tar' invocation. It represents
7238 something which ought to be told; ignoring what it means can cause very
7239 serious surprises, later.
7241 Some people, nevertheless, do not want to see this message. Wanting
7242 to play really dangerously, one may of course redirect `tar' standard
7243 error to the sink. For example, under `sh':
7245 $ tar -c -f archive.tar /home 2> /dev/null
7247 Another solution, both nicer and simpler, would be to change to the `/'
7248 directory first, and then avoid absolute notation. For example:
7250 $ tar -c -f archive.tar -C / home
7252 *Note Integrity::, for some of the security-related implications of
7255 ---------- Footnotes ----------
7257 (1) A side effect of this is that when `--create' is used with
7258 `--verbose' the resulting output is not, generally speaking, the same
7259 as the one you'd get running `tar --list' command. This may be
7260 important if you use some scripts for comparing both outputs. *Note
7261 listing member and file names::, for the information on how to handle
7265 File: tar.info, Node: Date input formats, Next: Formats, Prev: Choosing, Up: Top
7267 7 Date input formats
7268 ********************
7272 Our units of temporal measurement, from seconds on up to months,
7273 are so complicated, asymmetrical and disjunctive so as to make
7274 coherent mental reckoning in time all but impossible. Indeed, had
7275 some tyrannical god contrived to enslave our minds to time, to
7276 make it all but impossible for us to escape subjection to sodden
7277 routines and unpleasant surprises, he could hardly have done
7278 better than handing down our present system. It is like a set of
7279 trapezoidal building blocks, with no vertical or horizontal
7280 surfaces, like a language in which the simplest thought demands
7281 ornate constructions, useless particles and lengthy
7282 circumlocutions. Unlike the more successful patterns of language
7283 and science, which enable us to face experience boldly or at least
7284 level-headedly, our system of temporal calculation silently and
7285 persistently encourages our terror of time.
7287 ... It is as though architects had to measure length in feet,
7288 width in meters and height in ells; as though basic instruction
7289 manuals demanded a knowledge of five different languages. It is
7290 no wonder then that we often look into our own immediate past or
7291 future, last Tuesday or a week from Sunday, with feelings of
7292 helpless confusion. ...
7294 -- Robert Grudin, `Time and the Art of Living'.
7296 This section describes the textual date representations that GNU
7297 programs accept. These are the strings you, as a user, can supply as
7298 arguments to the various programs. The C interface (via the
7299 `parse_datetime' function) is not described here.
7303 * General date syntax:: Common rules.
7304 * Calendar date items:: 19 Dec 1994.
7305 * Time of day items:: 9:20pm.
7306 * Time zone items:: EST, PDT, GMT.
7307 * Day of week items:: Monday and others.
7308 * Relative items in date strings:: next tuesday, 2 years ago.
7309 * Pure numbers in date strings:: 19931219, 1440.
7310 * Seconds since the Epoch:: @1078100502.
7311 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
7312 * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al.
7315 File: tar.info, Node: General date syntax, Next: Calendar date items, Up: Date input formats
7317 7.1 General date syntax
7318 =======================
7320 A "date" is a string, possibly empty, containing many items separated
7321 by whitespace. The whitespace may be omitted when no ambiguity arises.
7322 The empty string means the beginning of today (i.e., midnight). Order
7323 of the items is immaterial. A date string may contain many flavors of
7326 * calendar date items
7332 * day of the week items
7338 We describe each of these item types in turn, below.
7340 A few ordinal numbers may be written out in words in some contexts.
7341 This is most useful for specifying day of the week items or relative
7342 items (see below). Among the most commonly used ordinal numbers, the
7343 word `last' stands for -1, `this' stands for 0, and `first' and `next'
7344 both stand for 1. Because the word `second' stands for the unit of
7345 time there is no way to write the ordinal number 2, but for convenience
7346 `third' stands for 3, `fourth' for 4, `fifth' for 5, `sixth' for 6,
7347 `seventh' for 7, `eighth' for 8, `ninth' for 9, `tenth' for 10,
7348 `eleventh' for 11 and `twelfth' for 12.
7350 When a month is written this way, it is still considered to be
7351 written numerically, instead of being "spelled in full"; this changes
7352 the allowed strings.
7354 In the current implementation, only English is supported for words
7355 and abbreviations like `AM', `DST', `EST', `first', `January',
7356 `Sunday', `tomorrow', and `year'.
7358 The output of the `date' command is not always acceptable as a date
7359 string, not only because of the language problem, but also because
7360 there is no standard meaning for time zone items like `IST'. When using
7361 `date' to generate a date string intended to be parsed later, specify a
7362 date format that is independent of language and that does not use time
7363 zone items other than `UTC' and `Z'. Here are some ways to do this:
7365 $ LC_ALL=C TZ=UTC0 date
7366 Mon Mar 1 00:21:42 UTC 2004
7367 $ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ'
7368 2004-03-01 00:21:42Z
7369 $ date --iso-8601=ns | tr T ' ' # --iso-8601 is a GNU extension.
7370 2004-02-29 16:21:42,692722128-0800
7371 $ date --rfc-2822 # a GNU extension
7372 Sun, 29 Feb 2004 16:21:42 -0800
7373 $ date +'%Y-%m-%d %H:%M:%S %z' # %z is a GNU extension.
7374 2004-02-29 16:21:42 -0800
7375 $ date +'@%s.%N' # %s and %N are GNU extensions.
7376 @1078100502.692722128
7378 Alphabetic case is completely ignored in dates. Comments may be
7379 introduced between round parentheses, as long as included parentheses
7380 are properly nested. Hyphens not followed by a digit are currently
7381 ignored. Leading zeros on numbers are ignored.
7383 Invalid dates like `2005-02-29' or times like `24:00' are rejected.
7384 In the typical case of a host that does not support leap seconds, a
7385 time like `23:59:60' is rejected even if it corresponds to a valid leap
7389 File: tar.info, Node: Calendar date items, Next: Time of day items, Prev: General date syntax, Up: Date input formats
7391 7.2 Calendar date items
7392 =======================
7394 A "calendar date item" specifies a day of the year. It is specified
7395 differently, depending on whether the month is specified numerically or
7396 literally. All these strings specify the same calendar date:
7398 1972-09-24 # ISO 8601.
7399 72-9-24 # Assume 19xx for 69 through 99,
7400 # 20xx for 00 through 68.
7401 72-09-24 # Leading zeros are ignored.
7402 9/24/72 # Common U.S. writing.
7404 24 Sept 72 # September has a special abbreviation.
7405 24 Sep 72 # Three-letter abbreviations always allowed.
7410 The year can also be omitted. In this case, the last specified year
7411 is used, or the current year if none. For example:
7418 For numeric months, the ISO 8601 format `YEAR-MONTH-DAY' is allowed,
7419 where YEAR is any positive number, MONTH is a number between 01 and 12,
7420 and DAY is a number between 01 and 31. A leading zero must be present
7421 if a number is less than ten. If YEAR is 68 or smaller, then 2000 is
7422 added to it; otherwise, if YEAR is less than 100, then 1900 is added to
7423 it. The construct `MONTH/DAY/YEAR', popular in the United States, is
7424 accepted. Also `MONTH/DAY', omitting the year.
7426 Literal months may be spelled out in full: `January', `February',
7427 `March', `April', `May', `June', `July', `August', `September',
7428 `October', `November' or `December'. Literal months may be abbreviated
7429 to their first three letters, possibly followed by an abbreviating dot.
7430 It is also permitted to write `Sept' instead of `September'.
7432 When months are written literally, the calendar date may be given as
7433 any of the following:
7440 Or, omitting the year:
7445 File: tar.info, Node: Time of day items, Next: Time zone items, Prev: Calendar date items, Up: Date input formats
7447 7.3 Time of day items
7448 =====================
7450 A "time of day item" in date strings specifies the time on a given day.
7451 Here are some examples, all of which represent the same time:
7456 20:02-0500 # In EST (U.S. Eastern Standard Time).
7458 More generally, the time of day may be given as
7459 `HOUR:MINUTE:SECOND', where HOUR is a number between 0 and 23, MINUTE
7460 is a number between 0 and 59, and SECOND is a number between 0 and 59
7461 possibly followed by `.' or `,' and a fraction containing one or more
7462 digits. Alternatively, `:SECOND' can be omitted, in which case it is
7463 taken to be zero. On the rare hosts that support leap seconds, SECOND
7466 If the time is followed by `am' or `pm' (or `a.m.' or `p.m.'), HOUR
7467 is restricted to run from 1 to 12, and `:MINUTE' may be omitted (taken
7468 to be zero). `am' indicates the first half of the day, `pm' indicates
7469 the second half of the day. In this notation, 12 is the predecessor of
7470 1: midnight is `12am' while noon is `12pm'. (This is the zero-oriented
7471 interpretation of `12am' and `12pm', as opposed to the old tradition
7472 derived from Latin which uses `12m' for noon and `12pm' for midnight.)
7474 The time may alternatively be followed by a time zone correction,
7475 expressed as `SHHMM', where S is `+' or `-', HH is a number of zone
7476 hours and MM is a number of zone minutes. The zone minutes term, MM,
7477 may be omitted, in which case the one- or two-digit correction is
7478 interpreted as a number of hours. You can also separate HH from MM
7479 with a colon. When a time zone correction is given this way, it forces
7480 interpretation of the time relative to Coordinated Universal Time
7481 (UTC), overriding any previous specification for the time zone or the
7482 local time zone. For example, `+0530' and `+05:30' both stand for the
7483 time zone 5.5 hours ahead of UTC (e.g., India). This is the best way to
7484 specify a time zone correction by fractional parts of an hour. The
7485 maximum zone correction is 24 hours.
7487 Either `am'/`pm' or a time zone correction may be specified, but not
7491 File: tar.info, Node: Time zone items, Next: Day of week items, Prev: Time of day items, Up: Date input formats
7496 A "time zone item" specifies an international time zone, indicated by a
7497 small set of letters, e.g., `UTC' or `Z' for Coordinated Universal
7498 Time. Any included periods are ignored. By following a
7499 non-daylight-saving time zone by the string `DST' in a separate word
7500 (that is, separated by some white space), the corresponding daylight
7501 saving time zone may be specified. Alternatively, a
7502 non-daylight-saving time zone can be followed by a time zone
7503 correction, to add the two values. This is normally done only for
7504 `UTC'; for example, `UTC+05:30' is equivalent to `+05:30'.
7506 Time zone items other than `UTC' and `Z' are obsolescent and are not
7507 recommended, because they are ambiguous; for example, `EST' has a
7508 different meaning in Australia than in the United States. Instead,
7509 it's better to use unambiguous numeric time zone corrections like
7510 `-0500', as described in the previous section.
7512 If neither a time zone item nor a time zone correction is supplied,
7513 time stamps are interpreted using the rules of the default time zone
7514 (*note Specifying time zone rules::).
7517 File: tar.info, Node: Day of week items, Next: Relative items in date strings, Prev: Time zone items, Up: Date input formats
7519 7.5 Day of week items
7520 =====================
7522 The explicit mention of a day of the week will forward the date (only
7523 if necessary) to reach that day of the week in the future.
7525 Days of the week may be spelled out in full: `Sunday', `Monday',
7526 `Tuesday', `Wednesday', `Thursday', `Friday' or `Saturday'. Days may
7527 be abbreviated to their first three letters, optionally followed by a
7528 period. The special abbreviations `Tues' for `Tuesday', `Wednes' for
7529 `Wednesday' and `Thur' or `Thurs' for `Thursday' are also allowed.
7531 A number may precede a day of the week item to move forward
7532 supplementary weeks. It is best used in expression like `third
7533 monday'. In this context, `last DAY' or `next DAY' is also acceptable;
7534 they move one week before or after the day that DAY by itself would
7537 A comma following a day of the week item is ignored.
7540 File: tar.info, Node: Relative items in date strings, Next: Pure numbers in date strings, Prev: Day of week items, Up: Date input formats
7542 7.6 Relative items in date strings
7543 ==================================
7545 "Relative items" adjust a date (or the current date if none) forward or
7546 backward. The effects of relative items accumulate. Here are some
7554 The unit of time displacement may be selected by the string `year'
7555 or `month' for moving by whole years or months. These are fuzzy units,
7556 as years and months are not all of equal duration. More precise units
7557 are `fortnight' which is worth 14 days, `week' worth 7 days, `day'
7558 worth 24 hours, `hour' worth 60 minutes, `minute' or `min' worth 60
7559 seconds, and `second' or `sec' worth one second. An `s' suffix on
7560 these units is accepted and ignored.
7562 The unit of time may be preceded by a multiplier, given as an
7563 optionally signed number. Unsigned numbers are taken as positively
7564 signed. No number at all implies 1 for a multiplier. Following a
7565 relative item by the string `ago' is equivalent to preceding the unit
7566 by a multiplier with value -1.
7568 The string `tomorrow' is worth one day in the future (equivalent to
7569 `day'), the string `yesterday' is worth one day in the past (equivalent
7572 The strings `now' or `today' are relative items corresponding to
7573 zero-valued time displacement, these strings come from the fact a
7574 zero-valued time displacement represents the current time when not
7575 otherwise changed by previous items. They may be used to stress other
7576 items, like in `12:00 today'. The string `this' also has the meaning
7577 of a zero-valued time displacement, but is preferred in date strings
7578 like `this thursday'.
7580 When a relative item causes the resulting date to cross a boundary
7581 where the clocks were adjusted, typically for daylight saving time, the
7582 resulting date and time are adjusted accordingly.
7584 The fuzz in units can cause problems with relative items. For
7585 example, `2003-07-31 -1 month' might evaluate to 2003-07-01, because
7586 2003-06-31 is an invalid date. To determine the previous month more
7587 reliably, you can ask for the month before the 15th of the current
7591 Thu, 31 Jul 2003 13:02:39 -0700
7592 $ date --date='-1 month' +'Last month was %B?'
7593 Last month was July?
7594 $ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!'
7595 Last month was June!
7597 Also, take care when manipulating dates around clock changes such as
7598 daylight saving leaps. In a few cases these have added or subtracted
7599 as much as 24 hours from the clock, so it is often wise to adopt
7600 universal time by setting the `TZ' environment variable to `UTC0'
7601 before embarking on calendrical calculations.
7604 File: tar.info, Node: Pure numbers in date strings, Next: Seconds since the Epoch, Prev: Relative items in date strings, Up: Date input formats
7606 7.7 Pure numbers in date strings
7607 ================================
7609 The precise interpretation of a pure decimal number depends on the
7610 context in the date string.
7612 If the decimal number is of the form YYYYMMDD and no other calendar
7613 date item (*note Calendar date items::) appears before it in the date
7614 string, then YYYY is read as the year, MM as the month number and DD as
7615 the day of the month, for the specified calendar date.
7617 If the decimal number is of the form HHMM and no other time of day
7618 item appears before it in the date string, then HH is read as the hour
7619 of the day and MM as the minute of the hour, for the specified time of
7620 day. MM can also be omitted.
7622 If both a calendar date and a time of day appear to the left of a
7623 number in the date string, but no relative item, then the number
7627 File: tar.info, Node: Seconds since the Epoch, Next: Specifying time zone rules, Prev: Pure numbers in date strings, Up: Date input formats
7629 7.8 Seconds since the Epoch
7630 ===========================
7632 If you precede a number with `@', it represents an internal time stamp
7633 as a count of seconds. The number can contain an internal decimal
7634 point (either `.' or `,'); any excess precision not supported by the
7635 internal representation is truncated toward minus infinity. Such a
7636 number cannot be combined with any other date item, as it specifies a
7637 complete time stamp.
7639 Internally, computer times are represented as a count of seconds
7640 since an epoch--a well-defined point of time. On GNU and POSIX
7641 systems, the epoch is 1970-01-01 00:00:00 UTC, so `@0' represents this
7642 time, `@1' represents 1970-01-01 00:00:01 UTC, and so forth. GNU and
7643 most other POSIX-compliant systems support such times as an extension
7644 to POSIX, using negative counts, so that `@-1' represents 1969-12-31
7647 Traditional Unix systems count seconds with 32-bit two's-complement
7648 integers and can represent times from 1901-12-13 20:45:52 through
7649 2038-01-19 03:14:07 UTC. More modern systems use 64-bit counts of
7650 seconds with nanosecond subcounts, and can represent all the times in
7651 the known lifetime of the universe to a resolution of 1 nanosecond.
7653 On most hosts, these counts ignore the presence of leap seconds.
7654 For example, on most hosts `@915148799' represents 1998-12-31 23:59:59
7655 UTC, `@915148800' represents 1999-01-01 00:00:00 UTC, and there is no
7656 way to represent the intervening leap second 1998-12-31 23:59:60 UTC.
7659 File: tar.info, Node: Specifying time zone rules, Next: Authors of parse_datetime, Prev: Seconds since the Epoch, Up: Date input formats
7661 7.9 Specifying time zone rules
7662 ==============================
7664 Normally, dates are interpreted using the rules of the current time
7665 zone, which in turn are specified by the `TZ' environment variable, or
7666 by a system default if `TZ' is not set. To specify a different set of
7667 default time zone rules that apply just to one date, start the date
7668 with a string of the form `TZ="RULE"'. The two quote characters (`"')
7669 must be present in the date, and any quotes or backslashes within RULE
7670 must be escaped by a backslash.
7672 For example, with the GNU `date' command you can answer the question
7673 "What time is it in New York when a Paris clock shows 6:30am on October
7674 31, 2004?" by using a date beginning with `TZ="Europe/Paris"' as shown
7675 in the following shell transcript:
7677 $ export TZ="America/New_York"
7678 $ date --date='TZ="Europe/Paris" 2004-10-31 06:30'
7679 Sun Oct 31 01:30:00 EDT 2004
7681 In this example, the `--date' operand begins with its own `TZ'
7682 setting, so the rest of that operand is processed according to
7683 `Europe/Paris' rules, treating the string `2004-10-31 06:30' as if it
7684 were in Paris. However, since the output of the `date' command is
7685 processed according to the overall time zone rules, it uses New York
7686 time. (Paris was normally six hours ahead of New York in 2004, but
7687 this example refers to a brief Halloween period when the gap was five
7690 A `TZ' value is a rule that typically names a location in the `tz'
7691 database (http://www.twinsun.com/tz/tz-link.htm). A recent catalog of
7692 location names appears in the TWiki Date and Time Gateway
7693 (http://twiki.org/cgi-bin/xtra/tzdate). A few non-GNU hosts require a
7694 colon before a location name in a `TZ' setting, e.g.,
7695 `TZ=":America/New_York"'.
7697 The `tz' database includes a wide variety of locations ranging from
7698 `Arctic/Longyearbyen' to `Antarctica/South_Pole', but if you are at sea
7699 and have your own private time zone, or if you are using a non-GNU host
7700 that does not support the `tz' database, you may need to use a POSIX
7701 rule instead. Simple POSIX rules like `UTC0' specify a time zone
7702 without daylight saving time; other rules can specify simple daylight
7703 saving regimes. *Note Specifying the Time Zone with `TZ': (libc)TZ
7707 File: tar.info, Node: Authors of parse_datetime, Prev: Specifying time zone rules, Up: Date input formats
7709 7.10 Authors of `parse_datetime'
7710 ================================
7712 `parse_datetime' started life as `getdate', as originally implemented
7713 by Steven M. Bellovin (<smb@research.att.com>) while at the University
7714 of North Carolina at Chapel Hill. The code was later tweaked by a
7715 couple of people on Usenet, then completely overhauled by Rich $alz
7716 (<rsalz@bbn.com>) and Jim Berets (<jberets@bbn.com>) in August, 1990.
7717 Various revisions for the GNU system were made by David MacKenzie, Jim
7718 Meyering, Paul Eggert and others, including renaming it to `get_date' to
7719 avoid a conflict with the alternative Posix function `getdate', and a
7720 later rename to `parse_datetime'. The Posix function `getdate' can
7721 parse more locale-specific dates using `strptime', but relies on an
7722 environment variable and external file, and lacks the thread-safety of
7725 This chapter was originally produced by Franc,ois Pinard
7726 (<pinard@iro.umontreal.ca>) from the `parse_datetime.y' source code,
7727 and then edited by K. Berry (<kb@cs.umb.edu>).
projects / tar / blob