1 .\" $FreeBSD: src/gnu/usr.bin/gzip/gzip.1,v 1.7 1999/09/20 09:15:15 phantom Exp $
2 .\" $DragonFly: src/gnu/usr.bin/gzip/Attic/gzip.1,v 1.2 2003/06/17 04:25:46 dillon Exp $
7 gzip, gunzip, zcat \- compress or expand files
11 .RB [ " \-acdfhlLnNrtvV19 " ]
19 .RB [ " \-acfhlLnNrtvV " ]
32 reduces the size of the named files using Lempel-Ziv coding (LZ77).
34 each file is replaced by one with the extension
36 while keeping the same ownership modes, access and modification times.
37 (The default extension is
41 for MSDOS, OS/2 FAT, Windows NT FAT and Atari.)
42 If no files are specified, or if a file name is "-", the standard input is
43 compressed to the standard output.
45 will only attempt to compress regular files.
46 In particular, it will ignore symbolic links.
48 If the compressed file name is too long for its file system,
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. For example, if file names are limited
55 to 14 characters, gzip.msdos.exe is compressed to gzi.msd.exe.gz.
56 Names are not truncated on systems which do not have a limit on file name
61 keeps the original file name and timestamp in the compressed file. These
62 are used when decompressing the file with the
64 option. This is useful when the compressed file name was truncated or
65 when the time stamp was not preserved after a file transfer.
67 Compressed files can be restored to their original form using
73 If the original name saved in the compressed file is not suitable for its
74 file system, a new name is constructed from the original one to make it
78 takes a list of files on its command line and replaces each
79 file whose name ends with .gz, -gz, .z, -z, _z or .Z
80 and which begins with the correct magic number with an uncompressed
81 file without the original extension.
83 also recognizes the special extensions
96 extension if necessary instead of truncating a file with a
101 can currently decompress files created by
102 .I gzip, zip, compress, compress -H
105 The detection of the input format is automatic. When using
106 the first two formats,
108 checks a 32 bit CRC. For
110 checks the uncompressed length. The standard
112 format was not designed to allow consistency checks. However
114 is sometimes able to detect a bad .Z file. If you get an error
115 when uncompressing a .Z file, do not assume that the .Z file is
116 correct simply because the standard
118 does not complain. This generally means that the standard
120 does not check its input, and happily generates garbage output.
121 The SCO compress -H format (lzh compression method) does not include a CRC
122 but also allows some consistency checks.
126 can be uncompressed by gzip only if they have a single member compressed
127 with the 'deflation' method. This feature is only intended to help
128 conversion of tar.zip files to the tar.gz format. To extract zip files
129 with several members, use
142 to preserve the original link to
145 uncompresses either a list of files on the command line or its
146 standard input and writes the uncompressed data on standard output.
148 will uncompress files that have the correct magic number whether
154 uses the Lempel-Ziv algorithm used in
157 The amount of compression obtained depends on the size of the
158 input and the distribution of common substrings.
159 Typically, text such as source code or English
160 is reduced by 60\-70%.
161 Compression is generally much better than that achieved by
164 Huffman coding (as used in
166 or adaptive Huffman coding
169 Compression is always performed, even if the compressed file is
170 slightly larger than the original. The worst case expansion is
171 a few bytes for the gzip file header, plus 5 bytes every 32K block,
172 or an expansion ratio of 0.015% for large files. Note that the actual
173 number of used disk blocks almost never increases.
175 preserves the mode, ownership and timestamps of files when compressing
181 ASCII text mode: convert end-of-lines using local conventions. This option
182 is supported only on some non-Unix systems. For MSDOS, CR LF is converted
183 to LF when compressing, and LF is converted to CR LF when decompressing.
185 .B \-c --stdout --to-stdout
186 Write output on standard output; keep original files unchanged.
187 If there are several input files, the output consists of a sequence of
188 independently compressed members. To obtain better compression,
189 concatenate all input files before compressing them.
191 .B \-d --decompress --uncompress
195 Force compression or decompression even if the file has multiple links
196 or the corresponding file already exists, or if the compressed data
197 is read from or written to a terminal. If the input data is not in
198 a format recognized by
200 and if the option --stdout is also given, copy the input data without change
201 to the standard output: let
208 and when not running in the background,
210 prompts to verify whether an existing file should be overwritten.
213 Display a help screen and quit.
216 For each compressed file, list the following fields:
218 compressed size: size of the compressed file
219 uncompressed size: size of the uncompressed file
220 ratio: compression ratio (0.0% if unknown)
221 uncompressed_name: name of the uncompressed file
223 The uncompressed size is given as -1 for files not in gzip format,
224 such as compressed .Z files. To get the uncompressed size for such a file,
229 In combination with the --verbose option, the following fields are also
232 method: compression method
233 crc: the 32-bit CRC of the uncompressed data
234 date & time: time stamp for the uncompressed file
236 The compression methods currently supported are deflate, compress, lzh
237 (SCO compress -H) and pack. The crc is given as ffffffff for a file
240 With --name, the uncompressed name, date and time are
241 those stored within the compress file if present.
243 With --verbose, the size totals and compression ratio for all files
244 is also displayed, unless some sizes are unknown. With --quiet,
245 the title and totals lines are not displayed.
253 When compressing, do not save the original file name and time stamp by
254 default. (The original name is always saved if the name had to be
255 truncated.) When decompressing, do not restore the original file name
256 if present (remove only the
258 suffix from the compressed file name) and do not restore the original
259 time stamp if present (copy it from the compressed file). This option
260 is the default when decompressing.
263 When compressing, always save the original file name and time stamp; this
264 is the default. When decompressing, restore the original file name and
265 time stamp if present. This option is useful on systems which have
266 a limit on file name length or when the time stamp has been lost after
270 Suppress all warnings.
273 Travel the directory structure recursively. If any of the file names
274 specified on the command line are directories,
276 will descend into the directory and compress all the files it finds there
277 (or decompress them in the case of
281 .B \-S .suf --suffix .suf
282 Use suffix .suf instead of .gz. Any suffix can be given, but suffixes
283 other than .z and .gz should be avoided to avoid confusion when files
284 are transferred to other systems. A null suffix forces gunzip to try
285 decompression on all given files regardless of suffix, as in:
287 gunzip -S "" * (*.* for MSDOS)
289 Previous versions of gzip used
290 the .z suffix. This was changed to avoid a conflict with
294 Test. Check the compressed file integrity.
297 Verbose. Display the name and percentage reduction for each file compressed
301 Version. Display the version number and compilation options then quit.
304 Regulate the speed of compression using the specified digit
310 indicates the fastest compression method (less compression)
315 indicates the slowest compression method (best compression).
316 The default compression level is
318 (that is, biased towards high compression at expense of speed).
320 Multiple compressed files can be concatenated. In this case,
322 will extract all members at once. For example:
324 gzip -c file1 > foo.gz
325 gzip -c file2 >> foo.gz
334 In case of damage to one member of a .gz file, other members can
335 still be recovered (if the damaged member is removed). However,
336 you can get better compression by compressing all members at once:
338 cat file1 file2 | gzip > foo.gz
340 compresses better than
342 gzip -c file1 file2 > foo.gz
344 If you want to recompress concatenated files to get better compression, do:
346 gzip -cd old.gz | gzip > new.gz
348 If a compressed file consists of several members, the uncompressed
349 size and CRC reported by the --list option applies to the last member
350 only. If you need the uncompressed size for all members, you can use:
352 gzip -cd file.gz | wc -c
354 If you wish to create a single archive file with multiple members so
355 that members can later be extracted independently, use an archiver
356 such as tar or zip. GNU tar supports the -z option to invoke gzip
357 transparently. gzip is designed as a complement to tar, not as a
360 The environment variable
362 can hold a set of default options for
364 These options are interpreted first and can be overwritten by
365 explicit command line parameters. For example:
366 for sh: GZIP="-8v --name"; export GZIP
367 for csh: setenv GZIP "-8v --name"
368 for MSDOS: set GZIP=-8v --name
370 On Vax/VMS, the name of the environment variable is GZIP_OPT, to
371 avoid a conflict with the symbol set for invocation of the program.
373 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), compress(1)
375 Exit status is normally 0;
376 if an error occurs, exit status is 1. If a warning occurs, exit status is 2.
378 Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
380 Invalid options were specified on the command line.
385 The file specified to
387 has not been compressed.
390 Corrupt input. Use zcat to recover some data.
392 The compressed file has been damaged. The data up to the point of failure
393 can be recovered using
400 bits, can only handle
405 was compressed (using LZW) by a program that could deal with
408 than the decompress code on this machine.
409 Recompress the file with gzip, which compresses better and uses
413 already has .gz suffix -- no change
415 The file is assumed to be already compressed.
416 Rename the file and try again.
419 already exists; do you wish to overwrite (y or n)?
421 Respond "y" if you want the output file to be replaced; "n" if not.
423 gunzip: corrupt input
425 A SIGSEGV violation was detected which usually means that the input file has
430 Percentage of the input saved by compression.
436 -- not a regular file or directory: ignored
438 When the input file is not a regular file or directory,
439 (e.g. a symbolic link, socket, FIFO, device file), it is
444 other links: unchanged
446 The input file has links; it is left unchanged. See
448 for more information. Use the
450 flag to force compression of multiply-linked files.
453 When writing compressed data to a tape, it is generally necessary to
454 pad the output with zeroes up to a block boundary. When the data is
455 read and the whole block is passed to
459 detects that there is extra trailing garbage after the compressed data
460 and emits a warning by default. You have to use the --quiet option to
461 suppress the warning. This option can be set in the
463 environment variable as in:
464 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
465 for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
467 In the above example, gzip is invoked implicitly by the -z option of
468 GNU tar. Make sure that the same block size (-b option of tar) is used
469 for reading and writing compressed data on tapes. (This example
470 assumes you are using the GNU version of tar.)
472 The --list option reports incorrect sizes if they exceed 2 gigabytes.
473 The --list option reports sizes as -1 and crc as ffffffff if the
474 compressed file is on a non seekable media.
476 In some rare cases, the --best option gives worse compression than
477 the default compression level (-6). On some highly redundant files,
479 compresses better than