3 gzip, gunzip, zcat \- compress or expand files
7 .RB [ " \-acdfhlLnNrtvV19 " ]
15 .RB [ " \-acfhlLnNrtvV " ]
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 For each compressed file, list the following fields:
224 compressed size: size of the compressed file
225 uncompressed size: size of the uncompressed file
226 ratio: compression ratio (0.0% if unknown)
227 uncompressed_name: name of the uncompressed file
229 The uncompressed size is given as -1 for files not in gzip format,
230 such as compressed .Z files. To get the uncompressed size for such a file,
235 In combination with the --verbose option, the following fields are also
238 method: compression method
239 crc: the 32-bit CRC of the uncompressed data
240 date & time: time stamp for the uncompressed file
242 The compression methods currently supported are deflate, compress, lzh
243 (SCO compress -H) and pack. The crc is given as ffffffff for a file
246 With --name, the uncompressed name, date and time are
247 those stored within the compress file if present.
249 With --verbose, the size totals and compression ratio for all files
250 is also displayed, unless some sizes are unknown. With --quiet,
251 the title and totals lines are not displayed.
259 When compressing, do not save the original file name and time stamp by
260 default. (The original name is always saved if the name had to be
261 truncated.) When decompressing, do not restore the original file name
262 if present (remove only the
264 suffix from the compressed file name) and do not restore the original
265 time stamp if present (copy it from the compressed file). This option
266 is the default when decompressing.
269 When compressing, always save the original file name and time stamp; this
270 is the default. When decompressing, restore the original file name and
271 time stamp if present. This option is useful on systems which have
272 a limit on file name length or when the time stamp has been lost after
276 Suppress all warnings.
279 Travel the directory structure recursively. If any of the file names
280 specified on the command line are directories,
282 will descend into the directory and compress all the files it finds there
283 (or decompress them in the case of
287 .B \-S .suf --suffix .suf
288 When compressing, use suffix .suf instead of .gz.
289 Any non-empty suffix can be given, but suffixes
290 other than .z and .gz should be avoided to avoid confusion when files
291 are transferred to other systems.
293 When decompressing, add .suf to the beginning of the list of
294 suffixes to try, when deriving an output file name from an input file name.
297 Test. Check the compressed file integrity.
300 Verbose. Display the name and percentage reduction for each file compressed
304 Version. Display the version number and compilation options then quit.
307 Regulate the speed of compression using the specified digit
313 indicates the fastest compression method (less compression)
318 indicates the slowest compression method (best compression).
319 The default compression level is
321 (that is, biased towards high compression at expense of speed).
323 Multiple compressed files can be concatenated. In this case,
325 will extract all members at once. For example:
327 gzip -c file1 > foo.gz
328 gzip -c file2 >> foo.gz
338 In case of damage to one member of a .gz file, other members can
339 still be recovered (if the damaged member is removed). However,
340 you can get better compression by compressing all members at once:
342 cat file1 file2 | gzip > foo.gz
344 compresses better than
346 gzip -c file1 file2 > foo.gz
348 If you want to recompress concatenated files to get better compression, do:
350 gzip -cd old.gz | gzip > new.gz
352 If a compressed file consists of several members, the uncompressed
353 size and CRC reported by the --list option applies to the last member
354 only. If you need the uncompressed size for all members, you can use:
356 gzip -cd file.gz | wc -c
358 If you wish to create a single archive file with multiple members so
359 that members can later be extracted independently, use an archiver
360 such as tar or zip. GNU tar supports the -z option to invoke gzip
361 transparently. gzip is designed as a complement to tar, not as a
364 The environment variable
366 can hold a set of default options for
368 These options are interpreted first and can be overwritten by
369 explicit command line parameters. For example:
370 for sh: GZIP="-8v --name"; export GZIP
371 for csh: setenv GZIP "-8v --name"
372 for MSDOS: set GZIP=-8v --name
374 On Vax/VMS, the name of the environment variable is GZIP_OPT, to
375 avoid a conflict with the symbol set for invocation of the program.
377 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1)
381 file format is specified in P. Deutsch, \s-1GZIP\s0 file format
382 specification version 4.3,
383 .BR <http://www.ietf.org/rfc/rfc1952.txt> ,
384 Internet RFC 1952 (May 1996).
387 deflation format is specified in P. Deutsch, \s-1DEFLATE\s0 Compressed
388 Data Format Specification version 1.3,
389 .BR <http://www.ietf.org/rfc/rfc1951.txt> ,
390 Internet RFC 1951 (May 1996).
392 Exit status is normally 0;
393 if an error occurs, exit status is 1. If a warning occurs, exit status is 2.
395 Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
396 Invalid options were specified on the command line.
398 \fIfile\fP\^: not in gzip format
399 The file specified to
401 has not been compressed.
403 \fIfile\fP\^: Corrupt input. Use zcat to recover some data.
404 The compressed file has been damaged. The data up to the point of failure
405 can be recovered using
407 zcat \fIfile\fP > recover
409 \fIfile\fP\^: compressed with \fIxx\fP bits, can only handle \fIyy\fP bits
411 was compressed (using LZW) by a program that could deal with
414 than the decompress code on this machine.
415 Recompress the file with gzip, which compresses better and uses
418 \fIfile\fP\^: already has .gz suffix -- no change
419 The file is assumed to be already compressed.
420 Rename the file and try again.
422 \fIfile\fP already exists; do you wish to overwrite (y or n)?
423 Respond "y" if you want the output file to be replaced; "n" if not.
425 gunzip: corrupt input
426 A SIGSEGV violation was detected which usually means that the input file has
429 \fIxx.x%\fP Percentage of the input saved by compression.
435 -- not a regular file or directory: ignored
436 When the input file is not a regular file or directory,
437 (e.g. a symbolic link, socket, FIFO, device file), it is
440 -- has \fIxx\fP other links: unchanged
441 The input file has links; it is left unchanged. See
443 for more information. Use the
445 flag to force compression of multiply-linked files.
447 When writing compressed data to a tape, it is generally necessary to
448 pad the output with zeroes up to a block boundary. When the data is
449 read and the whole block is passed to
453 detects that there is extra trailing garbage after the compressed data
454 and emits a warning by default. You have to use the --quiet option to
455 suppress the warning. This option can be set in the
457 environment variable as in:
458 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
459 for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
461 In the above example, gzip is invoked implicitly by the -z option of
462 GNU tar. Make sure that the same block size (-b option of tar) is used
463 for reading and writing compressed data on tapes. (This example
464 assumes you are using the GNU version of tar.)
466 The gzip format represents the input size modulo 2^32, so the
467 --list option reports incorrect uncompressed sizes and compression
468 ratios for uncompressed files 4 GB and larger. To work around this
469 problem, you can use the following command to discover a large
470 uncompressed file's true size:
474 The --list option reports sizes as -1 and crc as ffffffff if the
475 compressed file is on a non seekable media.
477 In some rare cases, the --best option gives worse compression than
478 the default compression level (-6). On some highly redundant files,
480 compresses better than
482 .SH "COPYRIGHT NOTICE"
483 Copyright \(co 1998, 1999, 2001, 2002, 2012 Free Software Foundation, Inc.
485 Copyright \(co 1992, 1993 Jean-loup Gailly
487 Permission is granted to make and distribute verbatim copies of
488 this manual provided the copyright notice and this permission notice
489 are preserved on all copies.
491 Permission is granted to process this file through troff and print the
492 results, provided the printed document carries copying permission
493 notice identical to this one except for the removal of this paragraph
494 (this paragraph not being relevant to the printed manual).
497 Permission is granted to copy and distribute modified versions of this
498 manual under the conditions for verbatim copying, provided that the entire
499 resulting derived work is distributed under the terms of a permission
500 notice identical to this one.
502 Permission is granted to copy and distribute translations of this manual
503 into another language, under the above conditions for modified versions,
504 except that this permission notice may be stated in a translation approved