1GZIP(1)                     General Commands Manual                    GZIP(1)
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3
4

NAME

6       gzip, gunzip, zcat - compress or expand files
7

SYNOPSIS

9       gzip [ -acdfhklLnNrtvV19 ] [-S suffix] [ name ...  ]
10       gunzip [ -acfhklLnNrtvV ] [-S suffix] [ name ...  ]
11       zcat [ -fhLV ] [ name ...  ]
12

DESCRIPTION

14       The  gzip  command reduces the size of the named files using Lempel-Ziv
15       coding (LZ77).  Whenever possible, each file is replaced  by  one  with
16       the  extension  .gz, while keeping the same ownership modes, access and
17       modification times.  (The default extension is z for MSDOS,  OS/2  FAT,
18       Windows  NT  FAT  and  Atari.)  If no files are specified, or if a file
19       name is "-", the standard input is compressed to the  standard  output.
20       The  gzip command will only attempt to compress regular files.  In par‐
21       ticular, it will ignore symbolic links.
22
23       If the compressed file name is too long for its file system, gzip trun‐
24       cates  it.  The gzip command attempts to truncate only the parts of the
25       file name longer than 3 characters.  (A part is delimited by dots.)  If
26       the name consists of small parts only, the longest parts are truncated.
27       For example, if file names are limited to 14 characters, gzip.msdos.exe
28       is  compressed  to  gzi.msd.exe.gz.  Names are not truncated on systems
29       which do not have a limit on file name length.
30
31       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
36       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
41       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
49       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
61       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  sev‐
66       eral members, use unzip instead of gunzip.
67
68       The zcat command is identical to gunzip -c.  (On some systems, zcat may
69       be 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
75       The gzip command uses the Lempel-Ziv algorithm used in zip  and  PKZIP.
76       The amount of compression obtained depends on the size of the input and
77       the distribution of common substrings.  Typically, text such as  source
78       code  or  English  is reduced by 60-70%.  Compression is generally much
79       better than that achieved by LZW (as used in compress), Huffman  coding
80       (as used in pack), or adaptive Huffman coding (compact).
81
82       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 per 32 KiB block, or an
85       expansion ratio of 0.015% for large files. The actual  number  of  used
86       disk blocks almost never increases.
87
88       gzip  normally  preserves the mode and modification timestamp of a file
89       when compressing or decompressing. If you have appropriate  privileges,
90       it also preserves the file's owner and group.
91

OPTIONS

93       -a --ascii
94              Ascii  text  mode: convert end-of-lines using local conventions.
95              This option is supported only on some non-Unix systems. For  MS‐
96              DOS,  CR  LF is converted to LF when compressing, and LF is con‐
97              verted to CR LF when decompressing.
98
99       -c --stdout --to-stdout
100              Write output on standard output; keep original files  unchanged.
101              If  there  are several input files, the output consists of a se‐
102              quence of independently compressed  members.  To  obtain  better
103              compression,  concatenate  all  input  files  before compressing
104              them.
105
106       -d --decompress --uncompress
107              Decompress.
108
109       -f --force
110              Force compression or decompression even if the file has multiple
111              links  or  the corresponding file already exists, or if the com‐
112              pressed data is read from or written to a terminal. If the input
113              data  is  not  in a format recognized by gzip, and if the option
114              --stdout is also given, copy the input data  without  change  to
115              the  standard  output:  let  zcat  behave  as cat.  If -f is not
116              given, and when not running in the background, gzip  prompts  to
117              verify whether an existing file should be overwritten.
118
119       -h --help
120              Display a help screen and quit.
121
122       -k --keep
123              Keep (don't delete) input files during compression or decompres‐
124              sion.
125
126       -l --list
127              For each compressed file, list the following fields:
128
129                  compressed size: size of the compressed file
130                  uncompressed size: size of the uncompressed file
131                  ratio: compression ratio (0.0% if unknown)
132                  uncompressed_name: name of the uncompressed file
133
134              The uncompressed size is given as -1 for files not in gzip  for‐
135              mat,  such  as compressed .Z files. To get the uncompressed size
136              for such a file, you can use:
137
138                  zcat file.Z | wc -c
139
140              In combination with the --verbose option, the  following  fields
141              are also displayed:
142
143                  method: compression method
144                  crc: the 32-bit CRC of the uncompressed data
145                  date & time: timestamp for the uncompressed file
146
147              The  compression  methods  currently supported are deflate, com‐
148              press, lzh (SCO compress -H) and pack.   The  crc  is  given  as
149              ffffffff for a file not in gzip format.
150
151              With  --name,  the  uncompressed name,  date and time  are those
152              stored within the compress file if present.
153
154              With --verbose, the size totals and compression  ratio  for  all
155              files  is  also  displayed,  unless some sizes are unknown. With
156              --quiet, the title and totals lines are not displayed.
157
158       -L --license
159              Display the gzip license and quit.
160
161       -n --no-name
162              When compressing, do not save the original file name  and  time‐
163              stamp by default. (The original name is always saved if the name
164              had to be truncated.) When decompressing,  do  not  restore  the
165              original  file name if present (remove only the gzip suffix from
166              the compressed file name) and do not restore the original  time‐
167              stamp if present (copy it from the compressed file). This option
168              is the default when decompressing.
169
170       -N --name
171              When compressing, always save the original file name,  and  save
172              the  seconds  part of the original modification timestamp if the
173              original is a regular file and  its  timestamp  is  at  least  1
174              (1970-01-01  00:00:01  UTC)  and  is less than 2**32 (2106-02-07
175              06:28:16 UTC, assuming leap seconds are not  counted);  this  is
176              the  default.  When  decompressing,  restore from the saved file
177              name and timestamp if present. This option is useful on  systems
178              which have a limit on file name length or when the timestamp has
179              been lost after a file transfer.
180
181       -q --quiet
182              Suppress all warnings.
183
184       -r --recursive
185              Travel the directory structure recursively. If any of  the  file
186              names  specified  on the command line are directories, gzip will
187              descend into the directory and compress all the files  it  finds
188              there (or decompress them in the case of gunzip ).
189
190       -S .suf --suffix .suf
191              When compressing, use suffix .suf instead of .gz.  Any non-empty
192              suffix can be given, but suffixes other than .z and  .gz  should
193              be  avoided  to  avoid  confusion  when files are transferred to
194              other systems.
195
196              When decompressing, add .suf to the beginning  of  the  list  of
197              suffixes to try, when deriving an output file name from an input
198              file name.
199
200       --synchronous
201              Use synchronous output.  With this option, gzip is  less  likely
202              to  lose  data during a system crash, but it can be considerably
203              slower.
204
205       -t --test
206              Test. Check the compressed file integrity then quit.
207
208       -v --verbose
209              Verbose. Display the name and percentage reduction for each file
210              compressed or decompressed.
211
212       -V --version
213              Version. Display the version number and compilation options then
214              quit.
215
216       -# --fast --best
217              Regulate the speed of compression using the specified  digit  #,
218              where  -1  or  --fast  indicates  the fastest compression method
219              (less compression) and -9 or --best indicates the  slowest  com‐
220              pression  method  (best  compression).   The default compression
221              level is -6 (that is, biased towards high compression at expense
222              of speed).
223
224       --rsyncable
225              When  you  synchronize  a compressed file between two computers,
226              this option allows  rsync  to  transfer  only  files  that  were
227              changed in the archive instead of the entire archive.  Normally,
228              after a change is made to any file in the archive, the  compres‐
229              sion  algorithm  can  generate a new version of the archive that
230              does not match the previous version  of  the  archive.  In  this
231              case,  rsync  transfers the entire new version of the archive to
232              the remote computer.  With this option, rsync can transfer  only
233              the  changed files as well as a small amount of metadata that is
234              required to update the archive structure in the  area  that  was
235              changed.
236

ADVANCED USAGE

238       Multiple  compressed  files  can  be concatenated. In this case, gunzip
239       will extract all members at once. For example:
240
241             gzip -c file1  > foo.gz
242             gzip -c file2 >> foo.gz
243
244       Then
245
246             gunzip -c foo
247
248       is equivalent to
249
250             cat file1 file2
251
252       In case of damage to one member of a .gz file, other members can  still
253       be  recovered  (if the damaged member is removed). However, you can get
254       better compression by compressing all members at once:
255
256             cat file1 file2 | gzip > foo.gz
257
258       compresses better than
259
260             gzip -c file1 file2 > foo.gz
261
262       If you want to recompress concatenated files to get better compression,
263       do:
264
265             gzip -cd old.gz | gzip > new.gz
266
267       If a compressed file consists of several members, the uncompressed size
268       and CRC reported by the --list option applies to the last member  only.
269       If you need the uncompressed size for all members, you can use:
270
271             gzip -cd file.gz | wc -c
272
273       If  you  wish  to create a single archive file with multiple members so
274       that members can later be extracted independently, use an archiver such
275       as  tar or zip. GNU tar supports the -z option to invoke gzip transpar‐
276       ently. gzip is designed as a complement to tar, not as a replacement.
277

ENVIRONMENT

279       The obsolescent environment variable GZIP can hold a set of default op‐
280       tions  for  gzip.  These options are interpreted first and can be over‐
281       written by explicit command line parameters.  As this can  cause  prob‐
282       lems  when  using  scripts,  this feature is supported only for options
283       that are reasonably likely to not cause too much harm, and  gzip  warns
284       if  it  is  used.   This feature will be removed in a future release of
285       gzip.
286
287       You can use an alias or script instead.  For example, if gzip is in the
288       directory /usr/bin you can prepend $HOME/bin to your PATH and create an
289       executable script $HOME/bin/gzip containing the following:
290
291             #! /bin/sh
292             export PATH=/usr/bin
293             exec gzip -9 "$@"
294

SEE ALSO

296       znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), com‐
297       press(1)
298
299       The gzip file format is specified in P. Deutsch, GZIP file format spec‐
300       ification version 4.3, <https://www.ietf.org/rfc/rfc1952.txt>, Internet
301       RFC  1952  (May  1996).   The  zip  deflation format is specified in P.
302       Deutsch, DEFLATE Compressed  Data  Format  Specification  version  1.3,
303       <https://www.ietf.org/rfc/rfc1951.txt>, Internet RFC 1951 (May 1996).
304

DIAGNOSTICS

306       Exit  status  is normally 0; if an error occurs, exit status is 1. If a
307       warning occurs, exit status is 2.
308
309       Usage: gzip [-cdfhklLnNrtvV19] [-S suffix] [file ...]
310              Invalid options were specified on the command line.
311
312       file: not in gzip format
313              The file specified to gunzip has not been compressed.
314
315       file: Corrupt input. Use zcat to recover some data.
316              The compressed file has been damaged. The data up to  the  point
317              of failure can be recovered using
318
319                    zcat file > recover
320
321       file: compressed with xx bits, can only handle yy bits
322              File  was  compressed  (using  LZW) by a program that could deal
323              with more bits than the decompress code on this machine.  Recom‐
324              press  the file with gzip, which compresses better and uses less
325              memory.
326
327       file: already has .gz suffix -- unchanged
328              The file is assumed to be already compressed.  Rename  the  file
329              and try again.
330
331       file already exists; do you wish to overwrite (y or n)?
332              Respond  "y"  if you want the output file to be replaced; "n" if
333              not.
334
335       gunzip: corrupt input
336              A SIGSEGV violation was detected which usually  means  that  the
337              input file has been corrupted.
338
339       xx.x% Percentage of the input saved by compression.
340              (Relevant only for -v and -l.)
341
342       -- not a regular file or directory: ignored
343              When  the input file is not a regular file or directory, (e.g. a
344              symbolic link, socket, FIFO, device file), it is left unaltered.
345
346       -- has xx other links: unchanged
347              The input file has links; it is left unchanged.  See  ln(1)  for
348              more information. Use the -f flag to force compression of multi‐
349              ply-linked files.
350

CAVEATS

352       When writing compressed data to a tape, it is  generally  necessary  to
353       pad  the  output  with  zeroes up to a block boundary. When the data is
354       read and the whole block is passed to gunzip for decompression,  gunzip
355       detects  that there is extra trailing garbage after the compressed data
356       and emits a warning by default.  You can use the --quiet option to sup‐
357       press the warning.
358

BUGS

360       In  some rare cases, the --best option gives worse compression than the
361       default compression level (-6). On some highly  redundant  files,  com‐
362       press compresses better than gzip.
363

REPORTING BUGS

365       Report bugs to: bug-gzip@gnu.org
366       GNU gzip home page: <https://www.gnu.org/software/gzip/>
367       General help using GNU software: <https://www.gnu.org/gethelp/>
368
370       Copyright © 1998-1999, 2001-2002, 2012, 2015-2022 Free Software Founda‐
371       tion, Inc.
372       Copyright © 1992, 1993 Jean-loup Gailly
373
374       Permission is granted to make and distribute verbatim  copies  of  this
375       manual  provided  the  copyright  notice and this permission notice are
376       preserved on all copies.
377
378       Permission is granted to copy and distribute modified versions of  this
379       manual under the conditions for verbatim copying, provided that the en‐
380       tire resulting derived work is distributed under the terms of a permis‐
381       sion notice identical to this one.
382
383       Permission  is granted to copy and distribute translations of this man‐
384       ual into another language, under the above conditions for modified ver‐
385       sions,  except  that this permission notice may be stated in a transla‐
386       tion approved by the Foundation.
387
388
389
390                                     local                             GZIP(1)
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