3 gzip, gunzip, zcat \- compress or expand files
7 .RB [ " \-acdfhlLnNrtvV19 " ]
15 .RB [ " \-acfhlLnNrtvV " ]
28 reduces the size of the named files using Lempel-Ziv coding (LZ77).
30 each file is replaced by one with the extension
32 while keeping the same ownership modes, access and modification times.
33 (The default extension is
37 for MSDOS, OS/2 FAT, Windows NT FAT and Atari.)
38 If no files are specified, or if a file name is "-", the standard input is
39 compressed to the standard output.
41 will only attempt to compress regular files.
42 In particular, it will ignore symbolic links.
44 If the compressed file name is too long for its file system,
48 attempts to truncate only the parts of the file name longer than 3 characters.
49 (A part is delimited by dots.) If the name consists of small parts only,
50 the longest parts are truncated. For example, if file names are limited
51 to 14 characters, gzip.msdos.exe is compressed to gzi.msd.exe.gz.
52 Names are not truncated on systems which do not have a limit on file name
57 keeps the original file name and timestamp in the compressed file. These
58 are used when decompressing the file with the
60 option. This is useful when the compressed file name was truncated or
61 when the time stamp was not preserved after a file transfer.
63 Compressed files can be restored to their original form using
69 If the original name saved in the compressed file is not suitable for its
70 file system, a new name is constructed from the original one to make it
74 takes a list of files on its command line and replaces each
75 file whose name ends with .gz, -gz, .z, -z, _z or .Z
76 and which begins with the correct magic number with an uncompressed
77 file without the original extension.
79 also recognizes the special extensions
92 extension if necessary instead of truncating a file with a
97 can currently decompress files created by
98 .I gzip, zip, compress, compress -H
101 The detection of the input format is automatic. When using
102 the first two formats,
104 checks a 32 bit CRC. For
106 checks the uncompressed length. The standard
108 format was not designed to allow consistency checks. However
110 is sometimes able to detect a bad .Z file. If you get an error
111 when uncompressing a .Z file, do not assume that the .Z file is
112 correct simply because the standard
114 does not complain. This generally means that the standard
116 does not check its input, and happily generates garbage output.
117 The SCO compress -H format (lzh compression method) does not include a CRC
118 but also allows some consistency checks.
122 can be uncompressed by gzip only if they have a single member compressed
123 with the 'deflation' method. This feature is only intended to help
124 conversion of tar.zip files to the tar.gz format. To extract a
126 file with a single member, use a command like
129 .IR "gunzip -S .zip foo.zip" .
131 with several members, use
144 to preserve the original link to
147 uncompresses either a list of files on the command line or its
148 standard input and writes the uncompressed data on standard output.
150 will uncompress files that have the correct magic number whether
156 uses the Lempel-Ziv algorithm used in
159 The amount of compression obtained depends on the size of the
160 input and the distribution of common substrings.
161 Typically, text such as source code or English
162 is reduced by 60\-70%.
163 Compression is generally much better than that achieved by
166 Huffman coding (as used in
168 or adaptive Huffman coding
171 Compression is always performed, even if the compressed file is
172 slightly larger than the original. The worst case expansion is
173 a few bytes for the gzip file header, plus 5 bytes every 32K block,
174 or an expansion ratio of 0.015% for large files. Note that the actual
175 number of used disk blocks almost never increases.
177 preserves the mode, ownership and timestamps of files when compressing
182 file format is specified in P. Deutsch, \s-1GZIP\s0 file format
183 specification version 4.3, <ftp://ftp.isi.edu/in-notes/rfc1952.txt>,
184 Internet RFC 1952 (May 1996). The
186 deflation format is specified in P. Deutsch, \s-1DEFLATE\s0 Compressed
187 Data Format Specification version 1.3,
188 <ftp://ftp.isi.edu/in-notes/rfc1951.txt>, Internet RFC 1951 (May 1996).
193 Ascii text mode: convert end-of-lines using local conventions. This option
194 is supported only on some non-Unix systems. For MSDOS, CR LF is converted
195 to LF when compressing, and LF is converted to CR LF when decompressing.
197 .B \-c --stdout --to-stdout
198 Write output on standard output; keep original files unchanged.
199 If there are several input files, the output consists of a sequence of
200 independently compressed members. To obtain better compression,
201 concatenate all input files before compressing them.
203 .B \-d --decompress --uncompress
207 Force compression or decompression even if the file has multiple links
208 or the corresponding file already exists, or if the compressed data
209 is read from or written to a terminal. If the input data is not in
210 a format recognized by
212 and if the option --stdout is also given, copy the input data without change
213 to the standard output: let
220 and when not running in the background,
222 prompts to verify whether an existing file should be overwritten.
225 Display a help screen and quit.
228 For each compressed file, list the following fields:
230 compressed size: size of the compressed file
231 uncompressed size: size of the uncompressed file
232 ratio: compression ratio (0.0% if unknown)
233 uncompressed_name: name of the uncompressed file
235 The uncompressed size is given as -1 for files not in gzip format,
236 such as compressed .Z files. To get the uncompressed size for such a file,
241 In combination with the --verbose option, the following fields are also
244 method: compression method
245 crc: the 32-bit CRC of the uncompressed data
246 date & time: time stamp for the uncompressed file
248 The compression methods currently supported are deflate, compress, lzh
249 (SCO compress -H) and pack. The crc is given as ffffffff for a file
252 With --name, the uncompressed name, date and time are
253 those stored within the compress file if present.
255 With --verbose, the size totals and compression ratio for all files
256 is also displayed, unless some sizes are unknown. With --quiet,
257 the title and totals lines are not displayed.
265 When compressing, do not save the original file name and time stamp by
266 default. (The original name is always saved if the name had to be
267 truncated.) When decompressing, do not restore the original file name
268 if present (remove only the
270 suffix from the compressed file name) and do not restore the original
271 time stamp if present (copy it from the compressed file). This option
272 is the default when decompressing.
275 When compressing, always save the original file name and time stamp; this
276 is the default. When decompressing, restore the original file name and
277 time stamp if present. This option is useful on systems which have
278 a limit on file name length or when the time stamp has been lost after
282 Suppress all warnings.
285 Travel the directory structure recursively. If any of the file names
286 specified on the command line are directories,
288 will descend into the directory and compress all the files it finds there
289 (or decompress them in the case of
294 While compressing, synchronize the output occasionally based on the input.
295 This increases size by less than 1 percent most cases, but means that the
297 program can much more efficiently synchronize files compressed with this flag.
299 cannot tell the difference between a compressed file created with this option,
300 and one created without it.
302 .B \-S .suf --suffix .suf
303 Use suffix .suf instead of .gz. Any suffix can be given, but suffixes
304 other than .z and .gz should be avoided to avoid confusion when files
305 are transferred to other systems. A null suffix forces gunzip to try
306 decompression on all given files regardless of suffix, as in:
308 gunzip -S "" * (*.* for MSDOS)
310 Previous versions of gzip used
311 the .z suffix. This was changed to avoid a conflict with
315 Test. Check the compressed file integrity.
318 Verbose. Display the name and percentage reduction for each file compressed
322 Version. Display the version number and compilation options then quit.
325 Regulate the speed of compression using the specified digit
331 indicates the fastest compression method (less compression)
336 indicates the slowest compression method (best compression).
337 The default compression level is
339 (that is, biased towards high compression at expense of speed).
341 Multiple compressed files can be concatenated. In this case,
343 will extract all members at once. For example:
345 gzip -c file1 > foo.gz
346 gzip -c file2 >> foo.gz
356 In case of damage to one member of a .gz file, other members can
357 still be recovered (if the damaged member is removed). However,
358 you can get better compression by compressing all members at once:
360 cat file1 file2 | gzip > foo.gz
362 compresses better than
364 gzip -c file1 file2 > foo.gz
366 If you want to recompress concatenated files to get better compression, do:
368 gzip -cd old.gz | gzip > new.gz
370 If a compressed file consists of several members, the uncompressed
371 size and CRC reported by the --list option applies to the last member
372 only. If you need the uncompressed size for all members, you can use:
374 gzip -cd file.gz | wc -c
376 If you wish to create a single archive file with multiple members so
377 that members can later be extracted independently, use an archiver
378 such as tar or zip. GNU tar supports the -z option to invoke gzip
379 transparently. gzip is designed as a complement to tar, not as a
382 The environment variable
384 can hold a set of default options for
386 These options are interpreted first and can be overwritten by
387 explicit command line parameters. For example:
388 for sh: GZIP="-8v --name"; export GZIP
389 for csh: setenv GZIP "-8v --name"
390 for MSDOS: set GZIP=-8v --name
392 On Vax/VMS, the name of the environment variable is GZIP_OPT, to
393 avoid a conflict with the symbol set for invocation of the program.
395 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1),
400 file format is specified in P. Deutsch, \s-1GZIP\s0 file format
401 specification version 4.3,
402 .BR <ftp://ftp.isi.edu/in-notes/rfc1952.txt> ,
403 Internet RFC 1952 (May 1996).
406 deflation format is specified in P. Deutsch, \s-1DEFLATE\s0 Compressed
407 Data Format Specification version 1.3,
408 .BR <ftp://ftp.isi.edu/in-notes/rfc1951.txt> ,
409 Internet RFC 1951 (May 1996).
411 Exit status is normally 0;
412 if an error occurs, exit status is 1. If a warning occurs, exit status is 2.
414 Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
415 Invalid options were specified on the command line.
417 \fIfile\fP\^: not in gzip format
418 The file specified to
420 has not been compressed.
422 \fIfile\fP\^: Corrupt input. Use zcat to recover some data.
423 The compressed file has been damaged. The data up to the point of failure
424 can be recovered using
426 zcat \fIfile\fP > recover
428 \fIfile\fP\^: compressed with \fIxx\fP bits, can only handle \fIyy\fP bits
430 was compressed (using LZW) by a program that could deal with
433 than the decompress code on this machine.
434 Recompress the file with gzip, which compresses better and uses
437 \fIfile\fP\^: already has .gz suffix -- no change
438 The file is assumed to be already compressed.
439 Rename the file and try again.
441 \fIfile\fP already exists; do you wish to overwrite (y or n)?
442 Respond "y" if you want the output file to be replaced; "n" if not.
444 gunzip: corrupt input
445 A SIGSEGV violation was detected which usually means that the input file has
448 \fIxx.x%\fP Percentage of the input saved by compression.
454 -- not a regular file or directory: ignored
455 When the input file is not a regular file or directory,
456 (e.g. a symbolic link, socket, FIFO, device file), it is
459 -- has \fIxx\fP other links: unchanged
460 The input file has links; it is left unchanged. See
462 for more information. Use the
464 flag to force compression of multiply-linked files.
466 When writing compressed data to a tape, it is generally necessary to
467 pad the output with zeroes up to a block boundary. When the data is
468 read and the whole block is passed to
472 detects that there is extra trailing garbage after the compressed data
473 and emits a warning by default. You have to use the --quiet option to
474 suppress the warning. This option can be set in the
476 environment variable as in:
477 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
478 for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
480 In the above example, gzip is invoked implicitly by the -z option of
481 GNU tar. Make sure that the same block size (-b option of tar) is used
482 for reading and writing compressed data on tapes. (This example
483 assumes you are using the GNU version of tar.)
485 The gzip format represents the input size modulo 2^32, so the
486 --list option reports incorrect uncompressed sizes and compression
487 ratios for uncompressed files 4 GB and larger. To work around this
488 problem, you can use the following command to discover a large
489 uncompressed file's true size:
493 The --list option reports sizes as -1 and crc as ffffffff if the
494 compressed file is on a non seekable media.
496 In some rare cases, the --best option gives worse compression than
497 the default compression level (-6). On some highly redundant files,
499 compresses better than
501 .SH "COPYRIGHT NOTICE"
502 Copyright \(co 1998, 1999, 2001, 2002 Free Software Foundation, Inc.
504 Copyright \(co 1992, 1993 Jean-loup Gailly
506 Permission is granted to make and distribute verbatim copies of
507 this manual provided the copyright notice and this permission notice
508 are preserved on all copies.
510 Permission is granted to process this file through troff and print the
511 results, provided the printed document carries copying permission
512 notice identical to this one except for the removal of this paragraph
513 (this paragraph not being relevant to the printed manual).
516 Permission is granted to copy and distribute modified versions of this
517 manual under the conditions for verbatim copying, provided that the entire
518 resulting derived work is distributed under the terms of a permission
519 notice identical to this one.
521 Permission is granted to copy and distribute translations of this manual
522 into another language, under the above conditions for modified versions,
523 except that this permission notice may be stated in a translation approved