1GZIP(1) General Commands Manual GZIP(1)
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6 gzip, gunzip, zcat - compress or expand files
7
9 gzip [ -acdfhklLnNrtvV19 ] [-S suffix] [ name ... ]
10 gunzip [ -acfhklLnNrtvV ] [-S suffix] [ name ... ]
11 zcat [ -fhLV ] [ name ... ]
12
14 Gzip reduces the size of the named files using Lempel-Ziv coding
15 (LZ77). Whenever possible, each file is replaced by one with the
16 extension .gz, while keeping the same ownership modes, access and modi‐
17 fication times. (The default extension is z for MSDOS, OS/2 FAT, Win‐
18 dows NT FAT and Atari.) If no files are specified, or if a file name
19 is "-", the standard input is compressed to the standard output. Gzip
20 will only attempt to compress regular files. In particular, it will
21 ignore symbolic links.
22 If the compressed file name is too long for its file system, gzip trun‐
24 cates it. Gzip attempts to truncate only the parts of the file name
25 longer than 3 characters. (A part is delimited by dots.) If the name
26 consists of small parts only, the longest parts are truncated. For
27 example, if file names are limited to 14 characters, gzip.msdos.exe is
28 compressed to gzi.msd.exe.gz. Names are not truncated on systems which
29 do not have a limit on file name length.
30 By default, gzip keeps the original file name and timestamp in the com‐
32 pressed file. These are used when decompressing the file with the -N
33 option. This is useful when the compressed file name was truncated or
34 when the timestamp was not preserved after a file transfer.
35 Compressed files can be restored to their original form using gzip -d
37 or gunzip or zcat. If the original name saved in the compressed file
38 is not suitable for its file system, a new name is constructed from the
39 original one to make it legal.
40 gunzip takes a list of files on its command line and replaces each file
42 whose name ends with .gz, -gz, .z, -z, or _z (ignoring case) and which
43 begins with the correct magic number with an uncompressed file without
44 the original extension. gunzip also recognizes the special extensions
45 .tgz and .taz as shorthands for .tar.gz and .tar.Z respectively. When
46 compressing, gzip uses the .tgz extension if necessary instead of trun‐
47 cating a file with a .tar extension.
48 gunzip can currently decompress files created by gzip, zip, compress,
50 compress -H or pack. The detection of the input format is automatic.
51 When using the first two formats, gunzip checks a 32 bit CRC. For pack
52 and gunzip checks the uncompressed length. The standard compress format
53 was not designed to allow consistency checks. However gunzip is some‐
54 times able to detect a bad .Z file. If you get an error when uncom‐
55 pressing a .Z file, do not assume that the .Z file is correct simply
56 because the standard uncompress does not complain. This generally means
57 that the standard uncompress does not check its input, and happily gen‐
58 erates garbage output. The SCO compress -H format (lzh compression
59 method) does not include a CRC but also allows some consistency checks.
60 Files created by zip can be uncompressed by gzip only if they have a
62 single member compressed with the 'deflation' method. This feature is
63 only intended to help conversion of tar.zip files to the tar.gz format.
64 To extract a zip file with a single member, use a command like gunzip
65 <foo.zip or gunzip -S .zip foo.zip. To extract zip files with several
66 members, use unzip instead of gunzip.
67 zcat is identical to gunzip -c. (On some systems, zcat may be
69 installed as gzcat to preserve the original link to compress.) zcat
70 uncompresses either a list of files on the command line or its standard
71 input and writes the uncompressed data on standard output. zcat will
72 uncompress files that have the correct magic number whether they have a
73 .gz suffix or not.
74 Gzip uses the Lempel-Ziv algorithm used in zip and PKZIP. The amount
76 of compression obtained depends on the size of the input and the dis‐
77 tribution of common substrings. Typically, text such as source code or
78 English is reduced by 60-70%. Compression is generally much better
79 than that achieved by LZW (as used in compress), Huffman coding (as
80 used in pack), or adaptive Huffman coding (compact).
81 Compression is always performed, even if the compressed file is
83 slightly larger than the original. The worst case expansion is a few
84 bytes for the gzip file header, plus 5 bytes every 32K block, or an
85 expansion ratio of 0.015% for large files. Note that the actual number
86 of used disk blocks almost never increases. gzip preserves the mode,
87 ownership and timestamps of files when compressing or decompressing.
88
90 -a --ascii
91 Ascii text mode: convert end-of-lines using local conventions.
92 This option is supported only on some non-Unix systems. For
93 MSDOS, CR LF is converted to LF when compressing, and LF is con‐
94 verted to CR LF when decompressing.
95 -c --stdout --to-stdout
97 Write output on standard output; keep original files unchanged.
98 If there are several input files, the output consists of a
99 sequence of independently compressed members. To obtain better
100 compression, concatenate all input files before compressing
101 them.
102 -d --decompress --uncompress
104 Decompress.
105 -f --force
107 Force compression or decompression even if the file has multiple
108 links or the corresponding file already exists, or if the com‐
109 pressed data is read from or written to a terminal. If the input
110 data is not in a format recognized by gzip, and if the option
111 --stdout is also given, copy the input data without change to
112 the standard output: let zcat behave as cat. If -f is not
113 given, and when not running in the background, gzip prompts to
114 verify whether an existing file should be overwritten.
115 -h --help
117 Display a help screen and quit.
118 -k --keep
120 Keep (don't delete) input files during compression or decompres‐
121 sion.
122 -l --list
124 For each compressed file, list the following fields:
125 compressed size: size of the compressed file
127 uncompressed size: size of the uncompressed file
128 ratio: compression ratio (0.0% if unknown)
129 uncompressed_name: name of the uncompressed file
130 The uncompressed size is given as -1 for files not in gzip for‐
132 mat, such as compressed .Z files. To get the uncompressed size
133 for such a file, you can use:
134 zcat file.Z | wc -c
136 In combination with the --verbose option, the following fields
138 are also displayed:
139 method: compression method
141 crc: the 32-bit CRC of the uncompressed data
142 date & time: timestamp for the uncompressed file
143 The compression methods currently supported are deflate, com‐
145 press, lzh (SCO compress -H) and pack. The crc is given as
146 ffffffff for a file not in gzip format.
147 With --name, the uncompressed name, date and time are those
149 stored within the compress file if present.
150 With --verbose, the size totals and compression ratio for all
152 files is also displayed, unless some sizes are unknown. With
153 --quiet, the title and totals lines are not displayed.
154 -L --license
156 Display the gzip license and quit.
157 -n --no-name
159 When compressing, do not save the original file name and time‐
160 stamp by default. (The original name is always saved if the name
161 had to be truncated.) When decompressing, do not restore the
162 original file name if present (remove only the gzip suffix from
163 the compressed file name) and do not restore the original time‐
164 stamp if present (copy it from the compressed file). This option
165 is the default when decompressing.
166 -N --name
168 When compressing, always save the original file name and time‐
169 stamp; this is the default. When decompressing, restore the
170 original file name and timestamp if present. This option is use‐
171 ful on systems which have a limit on file name length or when
172 the timestamp has been lost after a file transfer.
173 -q --quiet
175 Suppress all warnings.
176 -r --recursive
178 Travel the directory structure recursively. If any of the file
179 names specified on the command line are directories, gzip will
180 descend into the directory and compress all the files it finds
181 there (or decompress them in the case of gunzip ).
182 -S .suf --suffix .suf
184 When compressing, use suffix .suf instead of .gz. Any non-empty
185 suffix can be given, but suffixes other than .z and .gz should
186 be avoided to avoid confusion when files are transferred to
187 other systems.
188 When decompressing, add .suf to the beginning of the list of
190 suffixes to try, when deriving an output file name from an input
191 file name.
192 --synchronous
194 Use synchronous output. With this option, gzip is less likely
195 to lose data during a system crash, but it can be considerably
196 slower.
197 -t --test
199 Test. Check the compressed file integrity.
200 -v --verbose
202 Verbose. Display the name and percentage reduction for each file
203 compressed or decompressed.
204 -V --version
206 Version. Display the version number and compilation options then
207 quit.
208 -# --fast --best
210 Regulate the speed of compression using the specified digit #,
211 where -1 or --fast indicates the fastest compression method
212 (less compression) and -9 or --best indicates the slowest com‐
213 pression method (best compression). The default compression
214 level is -6 (that is, biased towards high compression at expense
215 of speed).
216 --rsyncable
218 When you synchronize a compressed file between two computers,
219 this option allows rsync to transfer only files that were
220 changed in the archive instead of the entire archive. Normally,
221 after a change is made to any file in the archive, the compres‐
222 sion algorithm can generate a new version of the archive that
223 does not match the previous version of the archive. In this
224 case, rsync transfers the entire new version of the archive to
225 the remote computer. With this option, rsync can transfer only
226 the changed files as well as a small amount of metadata that is
227 required to update the archive structure in the area that was
228 changed.
229
231 Multiple compressed files can be concatenated. In this case, gunzip
232 will extract all members at once. For example:
233 gzip -c file1 > foo.gz
235 gzip -c file2 >> foo.gz
236 Then
238 gunzip -c foo
240 is equivalent to
242 cat file1 file2
244 In case of damage to one member of a .gz file, other members can still
246 be recovered (if the damaged member is removed). However, you can get
247 better compression by compressing all members at once:
248 cat file1 file2 | gzip > foo.gz
250 compresses better than
252 gzip -c file1 file2 > foo.gz
254 If you want to recompress concatenated files to get better compression,
256 do:
257 gzip -cd old.gz | gzip > new.gz
259 If a compressed file consists of several members, the uncompressed size
261 and CRC reported by the --list option applies to the last member only.
262 If you need the uncompressed size for all members, you can use:
263 gzip -cd file.gz | wc -c
265 If you wish to create a single archive file with multiple members so
267 that members can later be extracted independently, use an archiver such
268 as tar or zip. GNU tar supports the -z option to invoke gzip transpar‐
269 ently. gzip is designed as a complement to tar, not as a replacement.
270
272 The obsolescent environment variable GZIP can hold a set of default
273 options for gzip. These options are interpreted first and can be over‐
274 written by explicit command line parameters. As this can cause prob‐
275 lems when using scripts, this feature is supported only for options
276 that are reasonably likely to not cause too much harm, and gzip warns
277 if it is used. This feature will be removed in a future release of
278 gzip.
279 You can use an alias or script instead. For example, if gzip is in the
281 directory /usr/bin you can prepend $HOME/bin to your PATH and create an
282 executable script $HOME/bin/gzip containing the following:
283 #! /bin/sh
285 export PATH=/usr/bin
286 exec gzip -9 "$@"
287
289 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), com‐
290 press(1)
291 The gzip file format is specified in P. Deutsch, GZIP file format spec‐
293 ification version 4.3, <https://www.ietf.org/rfc/rfc1952.txt>, Internet
294 RFC 1952 (May 1996). The zip deflation format is specified in P.
295 Deutsch, DEFLATE Compressed Data Format Specification version 1.3,
296 <https://www.ietf.org/rfc/rfc1951.txt>, Internet RFC 1951 (May 1996).
297
299 Exit status is normally 0; if an error occurs, exit status is 1. If a
300 warning occurs, exit status is 2.
301 Usage: gzip [-cdfhklLnNrtvV19] [-S suffix] [file ...]
303 Invalid options were specified on the command line.
304 file: not in gzip format
306 The file specified to gunzip has not been compressed.
307 file: Corrupt input. Use zcat to recover some data.
309 The compressed file has been damaged. The data up to the point
310 of failure can be recovered using
311 zcat file > recover
313 file: compressed with xx bits, can only handle yy bits
315 File was compressed (using LZW) by a program that could deal
316 with more bits than the decompress code on this machine. Recom‐
317 press the file with gzip, which compresses better and uses less
318 memory.
319 file: already has .gz suffix -- unchanged
321 The file is assumed to be already compressed. Rename the file
322 and try again.
323 file already exists; do you wish to overwrite (y or n)?
325 Respond "y" if you want the output file to be replaced; "n" if
326 not.
327 gunzip: corrupt input
329 A SIGSEGV violation was detected which usually means that the
330 input file has been corrupted.
331 xx.x% Percentage of the input saved by compression.
333 (Relevant only for -v and -l.)
334 -- not a regular file or directory: ignored
336 When the input file is not a regular file or directory, (e.g. a
337 symbolic link, socket, FIFO, device file), it is left unaltered.
338 -- has xx other links: unchanged
340 The input file has links; it is left unchanged. See ln(1) for
341 more information. Use the -f flag to force compression of multi‐
342 ply-linked files.
343
345 When writing compressed data to a tape, it is generally necessary to
346 pad the output with zeroes up to a block boundary. When the data is
347 read and the whole block is passed to gunzip for decompression, gunzip
348 detects that there is extra trailing garbage after the compressed data
349 and emits a warning by default. You can use the --quiet option to sup‐
350 press the warning.
351
353 The gzip format represents the input size modulo 2^32, so the --list
354 option reports incorrect uncompressed sizes and compression ratios for
355 uncompressed files 4 GB and larger. To work around this problem, you
356 can use the following command to discover a large uncompressed file's
357 true size:
358 zcat file.gz | wc -c
360 The --list option reports sizes as -1 and crc as ffffffff if the com‐
362 pressed file is on a non seekable media.
363 In some rare cases, the --best option gives worse compression than the
365 default compression level (-6). On some highly redundant files, com‐
366 press compresses better than gzip.
367
369 Copyright © 1998-1999, 2001-2002, 2012, 2015-2018 Free Software Founda‐
370 tion, Inc.
371 Copyright © 1992, 1993 Jean-loup Gailly
372 Permission is granted to make and distribute verbatim copies of this
374 manual provided the copyright notice and this permission notice are
375 preserved on all copies.
376 Permission is granted to copy and distribute modified versions of this
378 manual under the conditions for verbatim copying, provided that the
379 entire resulting derived work is distributed under the terms of a per‐
380 mission notice identical to this one.
381 Permission is granted to copy and distribute translations of this man‐
383 ual into another language, under the above conditions for modified ver‐
384 sions, except that this permission notice may be stated in a transla‐
385 tion approved by the Foundation.
386 local GZIP(1)