3 gzip, gunzip, zcat \- compress or expand files
7 .RB [ " \-acdfhklLnNrtvV19 " ]
15 .RB [ " \-acfhklLnNrtvV " ]
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, or _z (ignoring case)
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
104 The detection of the input format is automatic. When using
105 the first two formats,
107 checks a 32 bit CRC. For
111 checks the uncompressed length. The standard
113 format was not designed to allow consistency checks. However
115 is sometimes able to detect a bad .Z file. If you get an error
116 when uncompressing a .Z file, do not assume that the .Z file is
117 correct simply because the standard
119 does not complain. This generally means that the standard
121 does not check its input, and happily generates garbage output.
122 The SCO compress -H format (lzh compression method) does not include a CRC
123 but also allows some consistency checks.
127 can be uncompressed by gzip only if they have a single member compressed
128 with the 'deflation' method. This feature is only intended to help
129 conversion of tar.zip files to the tar.gz format. To extract a
131 file with a single member, use a command like
134 .IR "gunzip -S .zip foo.zip" .
136 with several members, use
149 to preserve the original link to
152 uncompresses either a list of files on the command line or its
153 standard input and writes the uncompressed data on standard output.
155 will uncompress files that have the correct magic number whether
161 uses the Lempel-Ziv algorithm used in
164 The amount of compression obtained depends on the size of the
165 input and the distribution of common substrings.
166 Typically, text such as source code or English
167 is reduced by 60\-70%.
168 Compression is generally much better than that achieved by
171 Huffman coding (as used in
173 or adaptive Huffman coding
176 Compression is always performed, even if the compressed file is
177 slightly larger than the original. The worst case expansion is
178 a few bytes for the gzip file header, plus 5 bytes every 32K block,
179 or an expansion ratio of 0.015% for large files. Note that the actual
180 number of used disk blocks almost never increases.
182 preserves the mode, ownership and timestamps of files when compressing
187 Ascii text mode: convert end-of-lines using local conventions. This option
188 is supported only on some non-Unix systems. For MSDOS, CR LF is converted
189 to LF when compressing, and LF is converted to CR LF when decompressing.
191 .B \-c --stdout --to-stdout
192 Write output on standard output; keep original files unchanged.
193 If there are several input files, the output consists of a sequence of
194 independently compressed members. To obtain better compression,
195 concatenate all input files before compressing them.
197 .B \-d --decompress --uncompress
201 Force compression or decompression even if the file has multiple links
202 or the corresponding file already exists, or if the compressed data
203 is read from or written to a terminal. If the input data is not in
204 a format recognized by
206 and if the option --stdout is also given, copy the input data without change
207 to the standard output: let
214 and when not running in the background,
216 prompts to verify whether an existing file should be overwritten.
219 Display a help screen and quit.
222 Keep (don't delete) input files during compression or decompression.
225 For each compressed file, list the following fields:
227 compressed size: size of the compressed file
228 uncompressed size: size of the uncompressed file
229 ratio: compression ratio (0.0% if unknown)
230 uncompressed_name: name of the uncompressed file
232 The uncompressed size is given as -1 for files not in gzip format,
233 such as compressed .Z files. To get the uncompressed size for such a file,
238 In combination with the --verbose option, the following fields are also
241 method: compression method
242 crc: the 32-bit CRC of the uncompressed data
243 date & time: time stamp for the uncompressed file
245 The compression methods currently supported are deflate, compress, lzh
246 (SCO compress -H) and pack. The crc is given as ffffffff for a file
249 With --name, the uncompressed name, date and time are
250 those stored within the compress file if present.
252 With --verbose, the size totals and compression ratio for all files
253 is also displayed, unless some sizes are unknown. With --quiet,
254 the title and totals lines are not displayed.
262 When compressing, do not save the original file name and time stamp by
263 default. (The original name is always saved if the name had to be
264 truncated.) When decompressing, do not restore the original file name
265 if present (remove only the
267 suffix from the compressed file name) and do not restore the original
268 time stamp if present (copy it from the compressed file). This option
269 is the default when decompressing.
272 When compressing, always save the original file name and time stamp; this
273 is the default. When decompressing, restore the original file name and
274 time stamp if present. This option is useful on systems which have
275 a limit on file name length or when the time stamp has been lost after
279 Suppress all warnings.
282 Travel the directory structure recursively. If any of the file names
283 specified on the command line are directories,
285 will descend into the directory and compress all the files it finds there
286 (or decompress them in the case of
290 .B \-S .suf --suffix .suf
291 When compressing, use suffix .suf instead of .gz.
292 Any non-empty suffix can be given, but suffixes
293 other than .z and .gz should be avoided to avoid confusion when files
294 are transferred to other systems.
296 When decompressing, add .suf to the beginning of the list of
297 suffixes to try, when deriving an output file name from an input file name.
300 Use synchronous output. With this option,
302 is less likely to lose data during a system crash, but it can be
306 Test. Check the compressed file integrity.
309 Verbose. Display the name and percentage reduction for each file compressed
313 Version. Display the version number and compilation options then quit.
316 Regulate the speed of compression using the specified digit
322 indicates the fastest compression method (less compression)
327 indicates the slowest compression method (best compression).
328 The default compression level is
330 (that is, biased towards high compression at expense of speed).
332 Multiple compressed files can be concatenated. In this case,
334 will extract all members at once. For example:
336 gzip -c file1 > foo.gz
337 gzip -c file2 >> foo.gz
347 In case of damage to one member of a .gz file, other members can
348 still be recovered (if the damaged member is removed). However,
349 you can get better compression by compressing all members at once:
351 cat file1 file2 | gzip > foo.gz
353 compresses better than
355 gzip -c file1 file2 > foo.gz
357 If you want to recompress concatenated files to get better compression, do:
359 gzip -cd old.gz | gzip > new.gz
361 If a compressed file consists of several members, the uncompressed
362 size and CRC reported by the --list option applies to the last member
363 only. If you need the uncompressed size for all members, you can use:
365 gzip -cd file.gz | wc -c
367 If you wish to create a single archive file with multiple members so
368 that members can later be extracted independently, use an archiver
369 such as tar or zip. GNU tar supports the -z option to invoke gzip
370 transparently. gzip is designed as a complement to tar, not as a
373 The obsolescent environment variable
375 can hold a set of default options for
377 These options are interpreted first and can be overwritten by explicit
378 command line parameters. As this can cause problems when using
379 scripts, this feature is supported only for options that are
380 reasonably likely to not cause too much harm, and
383 This feature will be removed in a future release of
386 You can use an alias or script instead. For example, if
394 and create an executable script
396 containing the following:
402 On VMS, the name of the obsolescent environment variable is GZIP_OPT, to
403 avoid a conflict with the symbol set for invocation of the program.
405 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1)
409 file format is specified in P. Deutsch, \s-1GZIP\s0 file format
410 specification version 4.3,
411 .BR <http://www.ietf.org/rfc/rfc1952.txt> ,
412 Internet RFC 1952 (May 1996).
415 deflation format is specified in P. Deutsch, \s-1DEFLATE\s0 Compressed
416 Data Format Specification version 1.3,
417 .BR <http://www.ietf.org/rfc/rfc1951.txt> ,
418 Internet RFC 1951 (May 1996).
420 Exit status is normally 0;
421 if an error occurs, exit status is 1. If a warning occurs, exit status is 2.
423 Usage: gzip [-cdfhklLnNrtvV19] [-S suffix] [file ...]
424 Invalid options were specified on the command line.
426 \fIfile\fP\^: not in gzip format
427 The file specified to
429 has not been compressed.
431 \fIfile\fP\^: Corrupt input. Use zcat to recover some data.
432 The compressed file has been damaged. The data up to the point of failure
433 can be recovered using
435 zcat \fIfile\fP > recover
437 \fIfile\fP\^: compressed with \fIxx\fP bits, can only handle \fIyy\fP bits
439 was compressed (using LZW) by a program that could deal with
442 than the decompress code on this machine.
443 Recompress the file with gzip, which compresses better and uses
446 \fIfile\fP\^: already has .gz suffix -- unchanged
447 The file is assumed to be already compressed.
448 Rename the file and try again.
450 \fIfile\fP already exists; do you wish to overwrite (y or n)?
451 Respond "y" if you want the output file to be replaced; "n" if not.
453 gunzip: corrupt input
454 A SIGSEGV violation was detected which usually means that the input file has
457 \fIxx.x%\fP Percentage of the input saved by compression.
463 -- not a regular file or directory: ignored
464 When the input file is not a regular file or directory,
465 (e.g. a symbolic link, socket, FIFO, device file), it is
468 -- has \fIxx\fP other links: unchanged
469 The input file has links; it is left unchanged. See
471 for more information. Use the
473 flag to force compression of multiply-linked files.
475 When writing compressed data to a tape, it is generally necessary to
476 pad the output with zeroes up to a block boundary. When the data is
477 read and the whole block is passed to
481 detects that there is extra trailing garbage after the compressed data
482 and emits a warning by default. You can use the --quiet option to
483 suppress the warning.
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, 2012, 2015-2016 Free Software Foundation,
505 Copyright \(co 1992, 1993 Jean-loup Gailly
507 Permission is granted to make and distribute verbatim copies of
508 this manual provided the copyright notice and this permission notice
509 are preserved on all copies.
511 Permission is granted to process this file through troff and print the
512 results, provided the printed document carries copying permission
513 notice identical to this one except for the removal of this paragraph
514 (this paragraph not being relevant to the printed manual).
517 Permission is granted to copy and distribute modified versions of this
518 manual under the conditions for verbatim copying, provided that the entire
519 resulting derived work is distributed under the terms of a permission
520 notice identical to this one.
522 Permission is granted to copy and distribute translations of this manual
523 into another language, under the above conditions for modified versions,
524 except that this permission notice may be stated in a translation approved