4 gzip, gunzip, zcat \- compress or expand files
8 .RB [ " \-acdfhlLnNrtvV19 " ]
16 .RB [ " \-acfhlLnNrtvV " ]
29 reduces the size of the named files using Lempel-Ziv coding (LZ77).
31 each file is replaced by one with the extension
33 while keeping the same ownership modes, access and modification times.
34 (The default extension is
38 for MSDOS, OS/2 FAT, Windows NT FAT and Atari.)
39 If no files are specified, or if a file name is "-", the standard input is
40 compressed to the standard output.
42 will only attempt to compress regular files.
43 In particular, it will ignore symbolic links.
45 If the compressed file name is too long for its file system,
49 attempts to truncate only the parts of the file name longer than 3 characters.
50 (A part is delimited by dots.) If the name consists of small parts only,
51 the longest parts are truncated. For example, if file names are limited
52 to 14 characters, gzip.msdos.exe is compressed to gzi.msd.exe.gz.
53 Names are not truncated on systems which do not have a limit on file name
58 keeps the original file name and timestamp in the compressed file. These
59 are used when decompressing the file with the
61 option. This is useful when the compressed file name was truncated or
62 when the time stamp was not preserved after a file transfer.
64 Compressed files can be restored to their original form using
70 If the original name saved in the compressed file is not suitable for its
71 file system, a new name is constructed from the original one to make it
75 takes a list of files on its command line and replaces each
76 file whose name ends with .gz, -gz, .z, -z, _z or .Z
77 and which begins with the correct magic number with an uncompressed
78 file without the original extension.
80 also recognizes the special extensions
93 extension if necessary instead of truncating a file with a
98 can currently decompress files created by
99 .I gzip, zip, compress, compress -H
102 The detection of the input format is automatic. When using
103 the first two formats,
105 checks a 32 bit CRC. For
107 checks the uncompressed length. The standard
109 format was not designed to allow consistency checks. However
111 is sometimes able to detect a bad .Z file. If you get an error
112 when uncompressing a .Z file, do not assume that the .Z file is
113 correct simply because the standard
115 does not complain. This generally means that the standard
117 does not check its input, and happily generates garbage output.
118 The SCO compress -H format (lzh compression method) does not include a CRC
119 but also allows some consistency checks.
123 can be uncompressed by gzip only if they have a single member compressed
124 with the 'deflation' method. This feature is only intended to help
125 conversion of tar.zip files to the tar.gz format. To extract zip files
126 with several members, use
139 to preserve the original link to
142 uncompresses either a list of files on the command line or its
143 standard input and writes the uncompressed data on standard output.
145 will uncompress files that have the correct magic number whether
151 uses the Lempel-Ziv algorithm used in
154 The amount of compression obtained depends on the size of the
155 input and the distribution of common substrings.
156 Typically, text such as source code or English
157 is reduced by 60\-70%.
158 Compression is generally much better than that achieved by
161 Huffman coding (as used in
163 or adaptive Huffman coding
166 Compression is always performed, even if the compressed file is
167 slightly larger than the original. The worst case expansion is
168 a few bytes for the gzip file header, plus 5 bytes every 32K block,
169 or an expansion ratio of 0.015% for large files. Note that the actual
170 number of used disk blocks almost never increases.
172 preserves the mode, ownership and timestamps of files when compressing
178 Ascii text mode: convert end-of-lines using local conventions. This option
179 is supported only on some non-Unix systems. For MSDOS, CR LF is converted
180 to LF when compressing, and LF is converted to CR LF when decompressing.
182 .B \-c --stdout --to-stdout
183 Write output on standard output; keep original files unchanged.
184 If there are several input files, the output consists of a sequence of
185 independently compressed members. To obtain better compression,
186 concatenate all input files before compressing them.
188 .B \-d --decompress --uncompress
192 Force compression or decompression even if the file has multiple links
193 or the corresponding file already exists, or if the compressed data
194 is read from or written to a terminal. If the input data is not in
195 a format recognized by
197 and if the option --stdout is also given, copy the input data without change
198 to the standard ouput: let
205 and when not running in the background,
207 prompts to verify whether an existing file should be overwritten.
210 Display a help screen and quit.
213 For each compressed file, list the following fields:
215 compressed size: size of the compressed file
216 uncompressed size: size of the uncompressed file
217 ratio: compression ratio (0.0% if unknown)
218 uncompressed_name: name of the uncompressed file
220 The uncompressed size is given as -1 for files not in gzip format,
221 such as compressed .Z files. To get the uncompressed size for such a file,
226 In combination with the --verbose option, the following fields are also
229 method: compression method
230 crc: the 32-bit CRC of the uncompressed data
231 date & time: time stamp for the uncompressed file
233 The compression methods currently supported are deflate, compress, lzh
234 (SCO compress -H) and pack. The crc is given as ffffffff for a file
237 With --name, the uncompressed name, date and time are
238 those stored within the compress file if present.
240 With --verbose, the size totals and compression ratio for all files
241 is also displayed, unless some sizes are unknown. With --quiet,
242 the title and totals lines are not displayed.
250 When compressing, do not save the original file name and time stamp by
251 default. (The original name is always saved if the name had to be
252 truncated.) When decompressing, do not restore the original file name
253 if present (remove only the
255 suffix from the compressed file name) and do not restore the original
256 time stamp if present (copy it from the compressed file). This option
257 is the default when decompressing.
260 When compressing, always save the original file name and time stamp; this
261 is the default. When decompressing, restore the original file name and
262 time stamp if present. This option is useful on systems which have
263 a limit on file name length or when the time stamp has been lost after
267 Suppress all warnings.
270 Travel the directory structure recursively. If any of the file names
271 specified on the command line are directories,
273 will descend into the directory and compress all the files it finds there
274 (or decompress them in the case of
278 .B \-S .suf --suffix .suf
279 Use suffix .suf instead of .gz. Any suffix can be given, but suffixes
280 other than .z and .gz should be avoided to avoid confusion when files
281 are transferred to other systems. A null suffix forces gunzip to try
282 decompression on all given files regardless of suffix, as in:
284 gunzip -S "" * (*.* for MSDOS)
286 Previous versions of gzip used
287 the .z suffix. This was changed to avoid a conflict with
291 Test. Check the compressed file integrity.
294 Verbose. Display the name and percentage reduction for each file compressed
298 Version. Display the version number and compilation options then quit.
301 Regulate the speed of compression using the specified digit
307 indicates the fastest compression method (less compression)
312 indicates the slowest compression method (best compression).
313 The default compression level is
315 (that is, biased towards high compression at expense of speed).
317 Multiple compressed files can be concatenated. In this case,
319 will extract all members at once. For example:
321 gzip -c file1 > foo.gz
322 gzip -c file2 >> foo.gz
331 In case of damage to one member of a .gz file, other members can
332 still be recovered (if the damaged member is removed). However,
333 you can get better compression by compressing all members at once:
335 cat file1 file2 | gzip > foo.gz
337 compresses better than
339 gzip -c file1 file2 > foo.gz
341 If you want to recompress concatenated files to get better compression, do:
343 gzip -cd old.gz | gzip > new.gz
345 If a compressed file consists of several members, the uncompressed
346 size and CRC reported by the --list option applies to the last member
347 only. If you need the uncompressed size for all members, you can use:
349 gzip -cd file.gz | wc -c
351 If you wish to create a single archive file with multiple members so
352 that members can later be extracted independently, use an archiver
353 such as tar or zip. GNU tar supports the -z option to invoke gzip
354 transparently. gzip is designed as a complement to tar, not as a
357 The environment variable
359 can hold a set of default options for
361 These options are interpreted first and can be overwritten by
362 explicit command line parameters. For example:
363 for sh: GZIP="-8v --name"; export GZIP
364 for csh: setenv GZIP "-8v --name"
365 for MSDOS: set GZIP=-8v --name
367 On Vax/VMS, the name of the environment variable is GZIP_OPT, to
368 avoid a conflict with the symbol set for invocation of the program.
370 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1),
373 Exit status is normally 0;
374 if an error occurs, exit status is 1. If a warning occurs, exit status is 2.
376 Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
378 Invalid options were specified on the command line.
383 The file specified to
385 has not been compressed.
388 Corrupt input. Use zcat to recover some data.
390 The compressed file has been damaged. The data up to the point of failure
391 can be recovered using
398 bits, can only handle
403 was compressed (using LZW) by a program that could deal with
406 than the decompress code on this machine.
407 Recompress the file with gzip, which compresses better and uses
411 already has .gz suffix -- no change
413 The file is assumed to be already compressed.
414 Rename the file and try again.
417 already exists; do you wish to overwrite (y or n)?
419 Respond "y" if you want the output file to be replaced; "n" if not.
421 gunzip: corrupt input
423 A SIGSEGV violation was detected which usually means that the input file has
428 Percentage of the input saved by compression.
434 -- 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
442 other links: unchanged
444 The input file has links; it is left unchanged. See
446 for more information. Use the
448 flag to force compression of multiply-linked files.
451 When writing compressed data to a tape, it is generally necessary to
452 pad the output with zeroes up to a block boundary. When the data is
453 read and the whole block is passed to
457 detects that there is extra trailing garbage after the compressed data
458 and emits a warning by default. You have to use the --quiet option to
459 suppress the warning. This option can be set in the
461 environment variable as in:
462 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
463 for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
465 In the above example, gzip is invoked implicitly by the -z option of
466 GNU tar. Make sure that the same block size (-b option of tar) is used
467 for reading and writing compressed data on tapes. (This example
468 assumes you are using the GNU version of tar.)
470 The --list option reports incorrect sizes if they exceed 2 gigabytes.
471 The --list option reports sizes as -1 and crc as ffffffff if the
472 compressed file is on a non seekable media.
474 In some rare cases, the --best option gives worse compression than
475 the default compression level (-6). On some highly redundant files,
477 compresses better than