| blob | d87db1d4edcbe0c63166cded10fb548a3a5ac2df |
1 .TH GZIP 1 local
2 .SH NAME
3 gzip, gunzip, zcat \- compress or expand files
4 .SH SYNOPSIS
5 .ll +8
6 .B gzip
7 .RB [ " \-acdfhklLnNrtvV19 " ]
8 .RB [ \-S\ suffix ]
9 [
10 .I "name \&..."
11 ]
12 .ll -8
13 .br
14 .B gunzip
15 .RB [ " \-acfhklLnNrtvV " ]
16 .RB [ \-S\ suffix ]
17 [
18 .I "name \&..."
19 ]
20 .br
21 .B zcat
22 .RB [ " \-fhLV " ]
23 [
24 .I "name \&..."
25 ]
26 .SH DESCRIPTION
27 The
28 .B gzip
29 command
30 reduces the size of the named files using Lempel-Ziv coding (LZ77).
31 Whenever possible,
32 each file is replaced by one with the extension
33 .BR "\&.gz" ,
34 while keeping the same ownership modes, access and modification times.
35 (The default extension is
36 .B "z"
37 for MSDOS, OS/2 FAT, Windows NT FAT and Atari.)
38 If no files are specified, or if a file name is "\-",
39 the standard input is compressed to the standard output.
40 The
41 .B gzip
42 command
43 will only attempt to compress regular files.
44 In particular, it will ignore symbolic links.
45 .PP
46 If the compressed file name is too long for its file system,
47 .B gzip
48 truncates it.
49 The
50 .B gzip
51 command
52 attempts to truncate only the parts of the file name longer than 3 characters.
53 (A part is delimited by dots.) If the name consists of small parts only,
54 the longest parts are truncated.
55 For example, if file names are limited to 14 characters,
56 gzip.msdos.exe is compressed to gzi.msd.exe.gz.
57 Names are not truncated on systems which do not have a limit on file name
58 length.
59 .PP
60 By default,
61 .B gzip
62 keeps the original file name and timestamp in the compressed file.
63 These are used when decompressing the file with the
64 .B \-N
65 option.
66 This is useful when the compressed file name was truncated or
67 when the timestamp was not preserved after a file transfer.
68 .PP
69 Compressed files can be restored to their original form using
70 .B "gzip \-d"
71 or
72 .B gunzip
73 or
74 .BR zcat .
75 If the original name saved in the compressed file is not suitable for its
76 file system, a new name is constructed from the original one to make it valid.
77 .PP
78 .B gunzip
79 takes a list of files on its command line and replaces each
80 file whose name ends with .gz, \-gz, .z, \-z, or _z (ignoring case)
81 and which begins with the correct magic number with an uncompressed
82 file without the original extension.
83 .B gunzip
84 also recognizes the special extensions
85 .B "\&.tgz"
86 and
87 .B "\&.taz"
88 as shorthands for
89 .B "\&.tar.gz"
90 and
91 .B "\&.tar.Z"
92 respectively.
93 When compressing,
94 .B gzip
95 uses the
96 .B "\&.tgz"
97 extension if necessary instead of truncating a file with a
98 .B "\&.tar"
99 extension.
100 .PP
101 .B gunzip
102 can currently decompress files created by
103 .BR gzip ,
104 .BR zip ,
105 .BR compress ,
106 .B "compress \-H"
107 or
108 .BR pack .
109 The detection of the input format is automatic.
110 When using the first two formats,
111 .B gunzip
112 checks a 32 bit CRC.
113 For
114 .B pack
115 and
116 .B gunzip
117 checks the uncompressed length.
118 The standard
119 .B compress
120 format was not designed to allow consistency checks.
121 However
122 .B gunzip
123 is sometimes able to detect a bad .Z file.
124 If you get an error when uncompressing a .Z file,
125 do not assume that the .Z file is
126 correct simply because the standard
127 .B uncompress
128 does not complain.
129 This generally means that the standard
130 .B uncompress
131 does not check its input, and happily generates garbage output.
132 The SCO compress \-H format (lzh compression method) does not include a CRC
133 but also allows some consistency checks.
134 .PP
135 Files created by
136 .B zip
137 can be uncompressed by gzip only if they have a single member compressed
138 with the 'deflation' method.
139 This feature is only intended to help
140 conversion of tar.zip files to the tar.gz format.
141 To extract a
142 .B zip
143 file with a single member, use a command like
144 .RB ' "gunzip <foo.zip" '
145 or
146 .RB ' "gunzip \-S .zip foo.zip" '.
147 To extract zip files
148 with several members, use
149 .B unzip
150 instead of
151 .BR gunzip .
152 .PP
153 The
154 .B zcat
155 command
156 is identical to
157 .B gunzip
158 .BR \-c .
159 (On some systems,
160 .B zcat
161 may be installed as
162 .B gzcat
163 to preserve the original link to
164 .BR compress .)
165 .B zcat
166 uncompresses either a list of files on the command line or its
167 standard input and writes the uncompressed data on standard output.
168 .B zcat
169 will uncompress files that have the correct magic number whether
170 they have a
171 .B "\&.gz"
172 suffix or not.
173 .PP
174 The
175 .B gzip
176 command
177 uses the Lempel-Ziv algorithm used in
178 .B zip
179 and PKZIP.
180 The amount of compression obtained depends on the size of the
181 input and the distribution of common substrings.
182 Typically, text such as source code or English
183 is reduced by 60\(en70%.
184 Compression is generally much better than that achieved by
185 LZW (as used in
186 .BR compress ),
187 Huffman coding (as used in
188 .BR pack ),
189 or adaptive Huffman coding
190 .RB ( compact ).
191 .PP
192 Compression is always performed, even if the compressed file is
193 slightly larger than the original.
194 The worst case expansion is
195 a few bytes for the gzip file header, plus 5 bytes per 32\ KiB block,
196 or an expansion ratio of 0.015% for large files.
197 The actual number of used disk blocks almost never increases.
198 .PP
199 .B gzip
200 normally preserves the mode and modification timestamp
201 of a file when compressing or decompressing.
202 If you have appropriate privileges,
203 it also preserves the file's owner and group.
204 .SH OPTIONS
205 .TP
206 .B \-a \-\-ascii
207 Ascii text mode: convert end-of-lines using local conventions.
208 This option is supported only on some non-Unix systems.
209 For MSDOS, CR LF is converted to LF when compressing,
210 and LF is converted to CR LF when decompressing.
211 .TP
212 .B \-c \-\-stdout \-\-to-stdout
213 Write output on standard output; keep original files unchanged.
214 If there are several input files, the output consists of a sequence of
215 independently compressed members.
216 To obtain better compression,
217 concatenate all input files before compressing them.
218 .TP
219 .B \-d \-\-decompress \-\-uncompress
220 Decompress.
221 .TP
222 .B \-f \-\-force
223 Force compression or decompression even if the file has multiple links
224 or the corresponding file already exists, or if the compressed data
225 is read from or written to a terminal.
226 If the input data is not in a format recognized by
227 .BR gzip ,
228 and if the option \-\-stdout is also given, copy the input data without change
229 to the standard output: let
230 .B zcat
231 behave as
232 .BR cat .
233 If
234 .B \-f
235 is not given,
236 and when not running in the background,
237 .B gzip
238 prompts to verify whether an existing file should be overwritten.
239 .TP
240 .B \-h \-\-help
241 Display a help screen and quit.
242 .TP
243 .B \-k \-\-keep
244 Keep (don't delete) input files during compression or decompression.
245 .TP
246 .B \-l \-\-list
247 For each compressed file, list the following fields:
249 compressed size: size of the compressed file
250 uncompressed size: size of the uncompressed file
251 ratio: compression ratio (0.0% if unknown)
252 uncompressed_name: name of the uncompressed file
254 The uncompressed size is given as \-1 for files not in gzip format,
255 such as compressed .Z files.
256 To get the uncompressed size for such a file, you can use:
258 zcat file.Z | wc \-c
260 In combination with the \-\-verbose option, the following fields are also
261 displayed:
263 method: compression method
264 crc: the 32-bit CRC of the uncompressed data
265 date & time: timestamp for the uncompressed file
267 The compression methods currently supported are deflate, compress, lzh
268 (SCO compress \-H) and pack.
269 The crc is given as ffffffff for a file not in gzip format.
271 With \-\-name, the uncompressed name, date and time are
272 those stored within the compress file if present.
274 With \-\-verbose, the size totals and compression ratio for all files
275 is also displayed, unless some sizes are unknown.
276 With \-\-quiet, the title and totals lines are not displayed.
277 .TP
278 .B \-L \-\-license
279 Display the
280 .B gzip
281 license and quit.
282 .TP
283 .B \-n \-\-no-name
284 When compressing, do not save the original file name and timestamp by default.
285 (The original name is always saved if the name had to be truncated.)
286 When decompressing, do not restore the original file name
287 if present (remove only the
288 .B gzip
289 suffix from the compressed file name) and do not restore the original
290 timestamp if present (copy it from the compressed file).
291 This option is the default when decompressing.
292 .TP
293 .B \-N \-\-name
294 When compressing, always save the original file name, and save
295 the seconds part of the original modification timestamp if the
296 original is a regular file and its timestamp is at least 1 (1970-01-01
297 00:00:01 UTC) and is less than 2**32 (2106-02-07 06:28:16 UTC,
298 assuming leap seconds are not counted); this
299 is the default.
300 When decompressing, restore from the saved file name and
301 timestamp if present.
302 This option is useful on systems which have a limit on file name
303 length or when the timestamp has been lost after a file transfer.
304 .TP
305 .B \-q \-\-quiet
306 Suppress all warnings.
307 .TP
308 .B \-r \-\-recursive
309 Travel the directory structure recursively.
310 If any of the file names specified on the command line are directories,
311 .B gzip
312 will descend into the directory and compress all the files it finds there
313 (or decompress them in the case of
314 .B gunzip
315 ).
316 .TP
317 .B \-S .suf \-\-suffix .suf
318 When compressing, use suffix .suf instead of .gz.
319 Although any non-empty suffix can be given so long as it does not contain "/",
320 suffixes other than .z and .gz should be avoided to avoid confusion when files
321 are transferred to other systems.
323 When decompressing, add .suf to the beginning of the list of
324 suffixes to try, when deriving an output file name from an input file name.
325 .TP
326 .B \-\-synchronous
327 Use synchronous output.
328 With this option,
329 .B gzip
330 is less likely to lose data during a system crash, but it can be
331 considerably slower.
332 .TP
333 .B \-t \-\-test
334 Test.
335 Check the compressed file integrity then quit.
336 .TP
337 .B \-v \-\-verbose
338 Verbose.
339 Display the name and percentage reduction for each file compressed
340 or decompressed.
341 .TP
342 .B \-V \-\-version
343 Version.
344 Display the version number and compilation options then quit.
345 .TP
346 .B \-# \-\-fast \-\-best
347 Regulate the speed of compression using the specified digit
348 .BR # ,
349 where
350 .B \-1
351 or
352 .B \-\-fast
353 indicates the fastest compression method (less compression)
354 and
355 .B \-9
356 or
357 .B \-\-best
358 indicates the slowest compression method (best compression).
359 The default compression level is
360 .B \-6
361 (that is, biased towards high compression at expense of speed).
362 .TP
363 .B \-\-rsyncable
364 When you synchronize a compressed file between two computers,
365 this option allows rsync to transfer only files that were changed in
366 the archive instead of the entire archive.
367 Normally, after a change is made to any file in the archive,
368 the compression algorithm can generate a new version of the archive
369 that does not match the previous version of the archive.
370 In this case, rsync transfers the entire new version of the archive to
371 the remote computer.
372 With this option, rsync can transfer only the changed files as well as
373 a small amount of metadata that is required to update the archive
374 structure in the area that was changed.
375 .SH "ADVANCED USAGE"
376 Multiple compressed files can be concatenated.
377 In this case,
378 .B gunzip
379 will extract all members at once.
380 For example:
382 gzip \-c file1 > foo.gz
383 gzip \-c file2 >> foo.gz
385 Then
387 gunzip \-c foo
389 is equivalent to
391 cat file1 file2
393 In case of damage to one member of a .gz file, other members can
394 still be recovered (if the damaged member is removed).
395 However, you can get better compression by compressing all members at once:
397 cat file1 file2 | gzip > foo.gz
399 compresses better than
401 gzip \-c file1 file2 > foo.gz
403 If you want to recompress concatenated files to get better compression, do:
405 gzip \-cd old.gz | gzip > new.gz
407 If a compressed file consists of several members, the uncompressed
408 size and CRC reported by the \-\-list option applies to the last member only.
409 If you need the uncompressed size for all members, you can use:
411 gzip \-cd file.gz | wc \-c
413 If you wish to create a single archive file with multiple members so
414 that members can later be extracted independently, use an archiver
415 such as tar or zip.
416 GNU tar supports the \-z option to invoke gzip transparently.
417 gzip is designed as a complement to tar, not as a replacement.
418 .SH "ENVIRONMENT"
419 The obsolescent environment variable
420 .B GZIP
421 can hold a set of default options for
422 .BR gzip .
423 These options are interpreted first and can be overwritten by explicit
424 command line parameters.
425 As this can cause problems when using scripts,
426 this feature is supported only for options that are
427 reasonably likely to not cause too much harm, and
428 .B gzip
429 warns if it is used.
430 This feature will be removed in a future release of
431 .BR gzip .
432 .PP
433 You can use an alias or script instead.
434 For example, if
435 .B gzip
436 is in the directory
437 .B /usr/bin
438 you can prepend
439 .B $HOME/bin
440 to your
441 .B PATH
442 and create an executable script
443 .B $HOME/bin/gzip
444 containing the following:
446 #! /bin/sh
447 export PATH=/usr/bin
448 exec gzip \-9 "$@"
449 .SH "SEE ALSO"
450 .BR znew (1),
451 .BR zcmp (1),
452 .BR zmore (1),
453 .BR zforce (1),
454 .BR gzexe (1),
455 .BR zip (1),
456 .BR unzip (1),
457 .BR compress (1)
458 .PP
459 The
460 .B gzip
461 file format is specified in P. Deutsch, \s-1GZIP\s0 file format
462 specification version 4.3,
463 .BR <https://www.ietf.org/rfc/rfc1952.txt> ,
464 Internet RFC 1952 (May 1996).
465 The
466 .B zip
467 deflation format is specified in P. Deutsch, \s-1DEFLATE\s0 Compressed
468 Data Format Specification version 1.3,
469 .BR <https://www.ietf.org/rfc/rfc1951.txt> ,
470 Internet RFC 1951 (May 1996).
471 .SH "DIAGNOSTICS"
472 Exit status is normally 0;
473 if an error occurs, exit status is 1.
474 If a warning occurs, exit status is 2.
475 .TP
476 Usage: gzip [\-cdfhklLnNrtvV19] [\-S suffix] [file ...]
477 Invalid options were specified on the command line.
478 .TP
479 \fIfile\fP\^: not in gzip format
480 The file specified to
481 .B gunzip
482 has not been compressed.
483 .TP
484 \fIfile\fP\^: Corrupt input.
485 Use zcat to recover some data.
486 The compressed file has been damaged.
487 The data up to the point of failure can be recovered using
489 zcat \fIfile\fP > recover
490 .TP
491 \fIfile\fP\^: compressed with \fIxx\fP bits, can only handle \fIyy\fP bits
492 .B File
493 was compressed (using LZW) by a program that could deal with
494 more
495 bits
496 than the decompress code on this machine.
497 Recompress the file with gzip, which compresses better and uses
498 less memory.
499 .TP
500 \fIfile\fP\^: already has .gz suffix \-\- unchanged
501 The file is assumed to be already compressed.
502 Rename the file and try again.
503 .TP
504 \fIfile\fP already exists; do you wish to overwrite (y or n)?
505 Respond "y" if you want the output file to be replaced; "n" if not.
506 .TP
507 gunzip: corrupt input
508 A SIGSEGV violation was detected which usually means that the input file has
509 been corrupted.
510 .TP
511 \fIxx.x%\fP Percentage of the input saved by compression.
512 (Relevant only for
513 .B \-v
514 and
515 .BR \-l \.)
516 .TP
517 \-\- not a regular file or directory: ignored
518 When the input file is not a regular file or directory,
519 (e.g., a symbolic link, socket, FIFO, device file), it is
520 left unaltered.
521 .TP
522 \-\- has \fIxx\fP other links: unchanged
523 The input file has links; it is left unchanged.
524 See
525 .BR ln "(1)"
526 for more information.
527 Use the
528 .B \-f
529 flag to force compression of multiply-linked files.
530 .SH CAVEATS
531 When writing compressed data to a tape, it is generally necessary to
532 pad the output with zeroes up to a block boundary.
533 When the data is read and the whole block is passed to
534 .B gunzip
535 for decompression,
536 .B gunzip
537 detects that there is extra trailing garbage after the compressed data
538 and emits a warning by default.
539 You can use the \-\-quiet option to suppress the warning.
540 .SH BUGS
541 In some rare cases, the \-\-best option gives worse compression than
542 the default compression level (\-6).
543 On some highly redundant files,
544 .B compress
545 compresses better than
546 .BR gzip .
547 .SH "REPORTING BUGS"
548 Report bugs to: bug\-gzip@gnu.org
549 .br
550 GNU gzip home page: <https://www.gnu.org/software/gzip/>
551 .br
552 General help using GNU software: <https://www.gnu.org/gethelp/>
553 .SH "COPYRIGHT NOTICE"
554 Copyright \(co 1998\(en1999, 2001\(en2002, 2012, 2015\(en2024 Free Software
555 Foundation, Inc.
556 .br
557 Copyright \(co 1992, 1993 Jean-loup Gailly
558 .PP
559 Permission is granted to make and distribute verbatim copies of
560 this manual provided the copyright notice and this permission notice
561 are preserved on all copies.
562 .ig
563 Permission is granted to process this file through troff and print the
564 results, provided the printed document carries copying permission
565 notice identical to this one except for the removal of this paragraph
566 (this paragraph not being relevant to the printed manual).
567 ..
568 .PP
569 Permission is granted to copy and distribute modified versions of this
570 manual under the conditions for verbatim copying, provided that the entire
571 resulting derived work is distributed under the terms of a permission
572 notice identical to this one.
573 .PP
574 Permission is granted to copy and distribute translations of this manual
575 into another language, under the above conditions for modified versions,
576 except that this permission notice may be stated in a translation approved
577 by the Foundation.