5 gzip, gunzip, zcat - compress or expand files
8 gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ... ]
9 gunzip [ -acfhlLnNrtvV ] [-S suffix] [ name ... ]
10 zcat [ -fhLV ] [ name ... ]
13 Gzip reduces the size of the named files using Lempel-Ziv
14 coding (LZ77). Whenever possible, each file is replaced by
15 one with the extension .gz, while keeping the same ownership
16 modes, access and modification times. (The default exten-
17 sion is -gz for VMS, z for MSDOS, OS/2 FAT, Windows NT FAT
18 and Atari.) If no files are specified, or if a file name is
19 "-", the standard input is compressed to the standard out-
20 put. Gzip will only attempt to compress regular files. In
21 particular, it will ignore symbolic links.
23 If the compressed file name is too long for its file system,
24 gzip truncates it. Gzip attempts to truncate only the parts
25 of the file name longer than 3 characters. (A part is
26 delimited by dots.) If the name consists of small parts
27 only, the longest parts are truncated. For example, if file
28 names are limited to 14 characters, gzip.msdos.exe is com-
29 pressed to gzi.msd.exe.gz. Names are not truncated on sys-
30 tems which do not have a limit on file name length.
32 By default, gzip keeps the original file name and timestamp
33 in the compressed file. These are used when decompressing
34 the file with the -N option. This is useful when the com-
35 pressed file name was truncated or when the time stamp was
36 not preserved after a file transfer.
38 Compressed files can be restored to their original form
39 using gzip -d or gunzip or zcat. If the original name saved
40 in the compressed file is not suitable for its file system,
41 a new name is constructed from the original one to make it
44 gunzip takes a list of files on its command line and
45 replaces each file whose name ends with .gz, -gz, .z, -z, _z
46 or .Z and which begins with the correct magic number with an
47 uncompressed file without the original extension. gunzip
48 also recognizes the special extensions .tgz and .taz as
49 shorthands for .tar.gz and .tar.Z respectively. When com-
50 pressing, gzip uses the .tgz extension if necessary instead
51 of truncating a file with a .tar extension.
53 gunzip can currently decompress files created by gzip, zip,
54 compress, compress -H or pack. The detection of the input
55 format is automatic. When using the first two formats,
57 SunOS 5.8 Last change: local 1
61 gunzip checks a 32 bit CRC. For pack, gunzip checks the
62 uncompressed length. The standard compress format was not
63 designed to allow consistency checks. However gunzip is
64 sometimes able to detect a bad .Z file. If you get an error
65 when uncompressing a .Z file, do not assume that the .Z file
66 is correct simply because the standard uncompress does not
67 complain. This generally means that the standard uncompress
68 does not check its input, and happily generates garbage out-
69 put. The SCO compress -H format (lzh compression method)
70 does not include a CRC but also allows some consistency
73 Files created by zip can be uncompressed by gzip only if
74 they have a single member compressed with the 'deflation'
75 method. This feature is only intended to help conversion of
76 tar.zip files to the tar.gz format. To extract zip files
77 with several members, use unzip instead of gunzip.
79 zcat is identical to gunzip -c. (On some systems, zcat may
80 be installed as gzcat to preserve the original link to com-
81 press.) zcat uncompresses either a list of files on the
82 command line or its standard input and writes the uncom-
83 pressed data on standard output. zcat will uncompress files
84 that have the correct magic number whether they have a .gz
87 Gzip uses the Lempel-Ziv algorithm used in zip and PKZIP.
88 The amount of compression obtained depends on the size of
89 the input and the distribution of common substrings. Typi-
90 cally, text such as source code or English is reduced by
91 60-70%. Compression is generally much better than that
92 achieved by LZW (as used in compress), Huffman coding (as
93 used in pack), or adaptive Huffman coding (compact).
95 Compression is always performed, even if the compressed file
96 is slightly larger than the original. The worst case expan-
97 sion is a few bytes for the gzip file header, plus 5 bytes
98 every 32K block, or an expansion ratio of 0.015% for large
99 files. Note that the actual number of used disk blocks
100 almost never increases. gzip preserves the mode, ownership
101 and timestamps of files when compressing or decompressing.
105 Ascii text mode: convert end-of-lines using local con-
106 ventions. This option is supported only on some non-
107 Unix systems. For MSDOS, CR LF is converted to LF when
108 compressing, and LF is converted to CR LF when decom-
111 -c --stdout --to-stdout
113 SunOS 5.8 Last change: local 2
115 User Commands GZIP(1)
117 Write output on standard output; keep original files
118 unchanged. If there are several input files, the out-
119 put consists of a sequence of independently compressed
120 members. To obtain better compression, concatenate all
121 input files before compressing them.
123 -d --decompress --uncompress
127 Force compression or decompression even if the file has
128 multiple links or the corresponding file already
129 exists, or if the compressed data is read from or writ-
130 ten to a terminal. If the input data is not in a format
131 recognized by gzip, and if the option --stdout is also
132 given, copy the input data without change to the stan-
133 dard ouput: let zcat behave as cat. If -f is not
134 given, and when not running in the background, gzip
135 prompts to verify whether an existing file should be
139 Display a help screen and quit.
142 For each compressed file, list the following fields:
144 compressed size: size of the compressed file
145 uncompressed size: size of the uncompressed file
146 ratio: compression ratio (0.0% if unknown)
147 uncompressed_name: name of the uncompressed file
149 The uncompressed size is given as -1 for files not in
150 gzip format, such as compressed .Z files. To get the
151 uncompressed size for such a file, you can use:
155 In combination with the --verbose option, the following
156 fields are also displayed:
158 method: compression method
159 crc: the 32-bit CRC of the uncompressed data
160 date & time: time stamp for the uncompressed file
162 The compression methods currently supported are
163 deflate, compress, lzh (SCO compress -H) and pack. The
164 crc is given as ffffffff for a file not in gzip format.
166 With --name, the uncompressed name, date and time are
167 those stored within the compress file if present.
169 SunOS 5.8 Last change: local 3
171 User Commands GZIP(1)
173 With --verbose, the size totals and compression ratio
174 for all files is also displayed, unless some sizes are
175 unknown. With --quiet, the title and totals lines are
179 Display the gzip license and quit.
182 When compressing, do not save the original file name
183 and time stamp by default. (The original name is always
184 saved if the name had to be truncated.) When decom-
185 pressing, do not restore the original file name if pre-
186 sent (remove only the gzip suffix from the compressed
187 file name) and do not restore the original time stamp
188 if present (copy it from the compressed file). This
189 option is the default when decompressing.
192 When compressing, always save the original file name
193 and time stamp; this is the default. When decompress-
194 ing, restore the original file name and time stamp if
195 present. This option is useful on systems which have a
196 limit on file name length or when the time stamp has
197 been lost after a file transfer.
200 Suppress all warnings.
203 Travel the directory structure recursively. If any of
204 the file names specified on the command line are direc-
205 tories, gzip will descend into the directory and com-
206 press all the files it finds there (or decompress them
207 in the case of gunzip ).
209 -S .suf --suffix .suf
210 Use suffix .suf instead of .gz. Any suffix can be
211 given, but suffixes other than .z and .gz should be
212 avoided to avoid confusion when files are transferred
213 to other systems. A null suffix forces gunzip to try
214 decompression on all given files regardless of suffix,
217 gunzip -S "" * (*.* for MSDOS)
219 Previous versions of gzip used the .z suffix. This was
220 changed to avoid a conflict with pack(1).
223 Test. Check the compressed file integrity.
225 SunOS 5.8 Last change: local 4
227 User Commands GZIP(1)
230 Verbose. Display the name and percentage reduction for
231 each file compressed or decompressed.
234 Version. Display the version number and compilation
238 Regulate the speed of compression using the specified
239 digit #, where -1 or --fast indicates the fastest com-
240 pression method (less compression) and -9 or --best
241 indicates the slowest compression method (best compres-
242 sion). The default compression level is -6 (that is,
243 biased towards high compression at expense of speed).
246 Multiple compressed files can be concatenated. In this case,
247 gunzip will extract all members at once. For example:
249 gzip -c file1 > foo.gz
250 gzip -c file2 >> foo.gz
260 In case of damage to one member of a .gz file, other members
261 can still be recovered (if the damaged member is removed).
262 However, you can get better compression by compressing all
265 cat file1 file2 | gzip > foo.gz
267 compresses better than
269 gzip -c file1 file2 > foo.gz
271 If you want to recompress concatenated files to get better
274 gzip -cd old.gz | gzip > new.gz
276 If a compressed file consists of several members, the uncom-
277 pressed size and CRC reported by the --list option applies
278 to the last member only. If you need the uncompressed size
279 for all members, you can use:
281 SunOS 5.8 Last change: local 5
283 User Commands GZIP(1)
285 gzip -cd file.gz | wc -c
287 If you wish to create a single archive file with multiple
288 members so that members can later be extracted indepen-
289 dently, use an archiver such as tar or zip. GNU tar supports
290 the -z option to invoke gzip transparently. gzip is designed
291 as a complement to tar, not as a replacement.
294 The environment variable GZIP can hold a set of default
295 options for gzip. These options are interpreted first and
296 can be overwritten by explicit command line parameters. For
298 for sh: GZIP="-8v --name"; export GZIP
299 for csh: setenv GZIP "-8v --name"
300 for MSDOS: set GZIP=-8v --name
302 On Vax/VMS, the name of the environment variable is
303 GZIP_OPT, to avoid a conflict with the symbol set for invo-
304 cation of the program.
307 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1),
308 unzip(1), compress(1), pack(1), compact(1)
310 The gzip file format is specified in P. Deutsch, GZIP file
311 format specification version 4.3, <ftp://ftp.isi.edu/in-
312 notes/rfc1952.txt>, Internet RFC 1952 (May 1996). The zip
313 deflation format is specified in P. Deutsch, DEFLATE Com-
314 pressed Data Format Specification version 1.3,
315 <ftp://ftp.isi.edu/in-notes/rfc1951.txt>, Internet RFC 1951
319 Exit status is normally 0; if an error occurs, exit status
320 is 1. If a warning occurs, exit status is 2.
322 Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
323 Invalid options were specified on the command line.
325 file: not in gzip format
326 The file specified to gunzip has not been compressed.
328 file: Corrupt input. Use zcat to recover some data.
329 The compressed file has been damaged. The data up to
330 the point of failure can be recovered using
334 file: compressed with xx bits, can only handle yy bits
335 File was compressed (using LZW) by a program that could
336 deal with more bits than the decompress code on this
338 SunOS 5.8 Last change: local 6
340 User Commands GZIP(1)
342 machine. Recompress the file with gzip, which com-
343 presses better and uses less memory.
345 file: already has .gz suffix -- no change
346 The file is assumed to be already compressed. Rename
347 the file and try again.
349 file already exists; do you wish to overwrite (y or n)?
350 Respond "y" if you want the output file to be replaced;
353 gunzip: corrupt input
354 A SIGSEGV violation was detected which usually means
355 that the input file has been corrupted.
357 xx.x% Percentage of the input saved by compression.
358 (Relevant only for -v and -l.)
360 -- not a regular file or directory: ignored
361 When the input file is not a regular file or directory,
362 (e.g. a symbolic link, socket, FIFO, device file), it
365 -- has xx other links: unchanged
366 The input file has links; it is left unchanged. See
367 ln(1) for more information. Use the -f flag to force
368 compression of multiply-linked files.
371 When writing compressed data to a tape, it is generally nec-
372 essary to pad the output with zeroes up to a block boundary.
373 When the data is read and the whole block is passed to gun-
374 zip for decompression, gunzip detects that there is extra
375 trailing garbage after the compressed data and emits a warn-
376 ing by default. You have to use the --quiet option to sup-
377 press the warning. This option can be set in the GZIP envi-
378 ronment variable as in:
379 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
380 for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
382 In the above example, gzip is invoked implicitly by the -z
383 option of GNU tar. Make sure that the same block size (-b
384 option of tar) is used for reading and writing compressed
385 data on tapes. (This example assumes you are using the GNU
389 The gzip format represents the the input size modulo 2^32,
390 so the --list option reports incorrect uncompressed sizes
391 and compression ratios for uncompressed files 4 GB and
392 larger. To work around this problem, you can use the fol-
393 lowing command to discover a large uncompressed file's true
395 SunOS 5.8 Last change: local 7
397 User Commands GZIP(1)
403 The --list option reports sizes as -1 and crc as ffffffff if
404 the compressed file is on a non seekable media.
406 In some rare cases, the --best option gives worse compres-
407 sion than the default compression level (-6). On some highly
408 redundant files, compress compresses better than gzip.
411 Copyright (C) 1998, 1999, 2001 Free Software Foundation,
413 Copyright (C) 1992, 1993 Jean-loup Gailly
415 Permission is granted to make and distribute verbatim copies
416 of this manual provided the copyright notice and this per-
417 mission notice are preserved on all copies.
419 Permission is granted to copy and distribute modified ver-
420 sions of this manual under the conditions for verbatim copy-
421 ing, provided that the entire resulting derived work is dis-
422 tributed under the terms of a permission notice identical to
425 Permission is granted to copy and distribute translations of
426 this manual into another language, under the above condi-
427 tions for modified versions, except that this permission
428 notice may be stated in a translation approved by the Foun-
431 SunOS 5.8 Last change: local 8
projects / gzip / blob