1 .\" $FreeBSD: src/gnu/usr.bin/gzip/gzip.1,v 1.7 1999/09/20 09:15:15 phantom Exp $
6 gzip, gunzip, zcat \- compress or expand files
10 .RB [ " \-acdfhlLnNrtvV19 " ]
18 .RB [ " \-acfhlLnNrtvV " ]
31 reduces the size of the named files using Lempel-Ziv coding (LZ77).
33 each file is replaced by one with the extension
35 while keeping the same ownership modes, access and modification times.
36 (The default extension is
40 for MSDOS, OS/2 FAT, Windows NT FAT and Atari.)
41 If no files are specified, or if a file name is "-", the standard input is
42 compressed to the standard output.
44 will only attempt to compress regular files.
45 In particular, it will ignore symbolic links.
47 If the compressed file name is too long for its file system,
51 attempts to truncate only the parts of the file name longer than 3 characters.
52 (A part is delimited by dots.) If the name consists of small parts only,
53 the longest parts are truncated. For example, if file names are limited
54 to 14 characters, gzip.msdos.exe is compressed to gzi.msd.exe.gz.
55 Names are not truncated on systems which do not have a limit on file name
60 keeps the original file name and timestamp in the compressed file. These
61 are used when decompressing the file with the
63 option. This is useful when the compressed file name was truncated or
64 when the time stamp was not preserved after a file transfer.
66 Compressed files can be restored to their original form using
72 If the original name saved in the compressed file is not suitable for its
73 file system, a new name is constructed from the original one to make it
77 takes a list of files on its command line and replaces each
78 file whose name ends with .gz, -gz, .z, -z, _z or .Z
79 and which begins with the correct magic number with an uncompressed
80 file without the original extension.
82 also recognizes the special extensions
95 extension if necessary instead of truncating a file with a
100 can currently decompress files created by
101 .I gzip, zip, compress, compress -H
104 The detection of the input format is automatic. When using
105 the first two formats,
107 checks a 32 bit CRC. For
109 checks the uncompressed length. The standard
111 format was not designed to allow consistency checks. However
113 is sometimes able to detect a bad .Z file. If you get an error
114 when uncompressing a .Z file, do not assume that the .Z file is
115 correct simply because the standard
117 does not complain. This generally means that the standard
119 does not check its input, and happily generates garbage output.
120 The SCO compress -H format (lzh compression method) does not include a CRC
121 but also allows some consistency checks.
125 can be uncompressed by gzip only if they have a single member compressed
126 with the 'deflation' method. This feature is only intended to help
127 conversion of tar.zip files to the tar.gz format. To extract zip files
128 with several members, use
141 to preserve the original link to
144 uncompresses either a list of files on the command line or its
145 standard input and writes the uncompressed data on standard output.
147 will uncompress files that have the correct magic number whether
153 uses the Lempel-Ziv algorithm used in
156 The amount of compression obtained depends on the size of the
157 input and the distribution of common substrings.
158 Typically, text such as source code or English
159 is reduced by 60\-70%.
160 Compression is generally much better than that achieved by
163 Huffman coding (as used in
165 or adaptive Huffman coding
168 Compression is always performed, even if the compressed file is
169 slightly larger than the original. The worst case expansion is
170 a few bytes for the gzip file header, plus 5 bytes every 32K block,
171 or an expansion ratio of 0.015% for large files. Note that the actual
172 number of used disk blocks almost never increases.
174 preserves the mode, ownership and timestamps of files when compressing
180 ASCII text mode: convert end-of-lines using local conventions. This option
181 is supported only on some non-Unix systems. For MSDOS, CR LF is converted
182 to LF when compressing, and LF is converted to CR LF when decompressing.
184 .B \-c --stdout --to-stdout
185 Write output on standard output; keep original files unchanged.
186 If there are several input files, the output consists of a sequence of
187 independently compressed members. To obtain better compression,
188 concatenate all input files before compressing them.
190 .B \-d --decompress --uncompress
194 Force compression or decompression even if the file has multiple links
195 or the corresponding file already exists, or if the compressed data
196 is read from or written to a terminal. If the input data is not in
197 a format recognized by
199 and if the option --stdout is also given, copy the input data without change
200 to the standard output: let
207 and when not running in the background,
209 prompts to verify whether an existing file should be overwritten.
212 Display a help screen and quit.
215 For each compressed file, list the following fields:
217 compressed size: size of the compressed file
218 uncompressed size: size of the uncompressed file
219 ratio: compression ratio (0.0% if unknown)
220 uncompressed_name: name of the uncompressed file
222 The uncompressed size is given as -1 for files not in gzip format,
223 such as compressed .Z files. To get the uncompressed size for such a file,
228 In combination with the --verbose option, the following fields are also
231 method: compression method
232 crc: the 32-bit CRC of the uncompressed data
233 date & time: time stamp for the uncompressed file
235 The compression methods currently supported are deflate, compress, lzh
236 (SCO compress -H) and pack. The crc is given as ffffffff for a file
239 With --name, the uncompressed name, date and time are
240 those stored within the compress file if present.
242 With --verbose, the size totals and compression ratio for all files
243 is also displayed, unless some sizes are unknown. With --quiet,
244 the title and totals lines are not displayed.
252 When compressing, do not save the original file name and time stamp by
253 default. (The original name is always saved if the name had to be
254 truncated.) When decompressing, do not restore the original file name
255 if present (remove only the
257 suffix from the compressed file name) and do not restore the original
258 time stamp if present (copy it from the compressed file). This option
259 is the default when decompressing.
262 When compressing, always save the original file name and time stamp; this
263 is the default. When decompressing, restore the original file name and
264 time stamp if present. This option is useful on systems which have
265 a limit on file name length or when the time stamp has been lost after
269 Suppress all warnings.
272 Travel the directory structure recursively. If any of the file names
273 specified on the command line are directories,
275 will descend into the directory and compress all the files it finds there
276 (or decompress them in the case of
280 .B \-S .suf --suffix .suf
281 Use suffix .suf instead of .gz. Any suffix can be given, but suffixes
282 other than .z and .gz should be avoided to avoid confusion when files
283 are transferred to other systems. A null suffix forces gunzip to try
284 decompression on all given files regardless of suffix, as in:
286 gunzip -S "" * (*.* for MSDOS)
288 Previous versions of gzip used
289 the .z suffix. This was changed to avoid a conflict with
293 Test. Check the compressed file integrity.
296 Verbose. Display the name and percentage reduction for each file compressed
300 Version. Display the version number and compilation options then quit.
303 Regulate the speed of compression using the specified digit
309 indicates the fastest compression method (less compression)
314 indicates the slowest compression method (best compression).
315 The default compression level is
317 (that is, biased towards high compression at expense of speed).
319 Multiple compressed files can be concatenated. In this case,
321 will extract all members at once. For example:
323 gzip -c file1 > foo.gz
324 gzip -c file2 >> foo.gz
333 In case of damage to one member of a .gz file, other members can
334 still be recovered (if the damaged member is removed). However,
335 you can get better compression by compressing all members at once:
337 cat file1 file2 | gzip > foo.gz
339 compresses better than
341 gzip -c file1 file2 > foo.gz
343 If you want to recompress concatenated files to get better compression, do:
345 gzip -cd old.gz | gzip > new.gz
347 If a compressed file consists of several members, the uncompressed
348 size and CRC reported by the --list option applies to the last member
349 only. If you need the uncompressed size for all members, you can use:
351 gzip -cd file.gz | wc -c
353 If you wish to create a single archive file with multiple members so
354 that members can later be extracted independently, use an archiver
355 such as tar or zip. GNU tar supports the -z option to invoke gzip
356 transparently. gzip is designed as a complement to tar, not as a
359 The environment variable
361 can hold a set of default options for
363 These options are interpreted first and can be overwritten by
364 explicit command line parameters. For example:
365 for sh: GZIP="-8v --name"; export GZIP
366 for csh: setenv GZIP "-8v --name"
367 for MSDOS: set GZIP=-8v --name
369 On Vax/VMS, the name of the environment variable is GZIP_OPT, to
370 avoid a conflict with the symbol set for invocation of the program.
372 znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), compress(1)
374 Exit status is normally 0;
375 if an error occurs, exit status is 1. If a warning occurs, exit status is 2.
377 Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
379 Invalid options were specified on the command line.
384 The file specified to
386 has not been compressed.
389 Corrupt input. Use zcat to recover some data.
391 The compressed file has been damaged. The data up to the point of failure
392 can be recovered using
399 bits, can only handle
404 was compressed (using LZW) by a program that could deal with
407 than the decompress code on this machine.
408 Recompress the file with gzip, which compresses better and uses
412 already has .gz suffix -- no change
414 The file is assumed to be already compressed.
415 Rename the file and try again.
418 already exists; do you wish to overwrite (y or n)?
420 Respond "y" if you want the output file to be replaced; "n" if not.
422 gunzip: corrupt input
424 A SIGSEGV violation was detected which usually means that the input file has
429 Percentage of the input saved by compression.
435 -- not a regular file or directory: ignored
437 When the input file is not a regular file or directory,
438 (e.g. a symbolic link, socket, FIFO, device file), it is
443 other links: unchanged
445 The input file has links; it is left unchanged. See
447 for more information. Use the
449 flag to force compression of multiply-linked files.
452 When writing compressed data to a tape, it is generally necessary to
453 pad the output with zeroes up to a block boundary. When the data is
454 read and the whole block is passed to
458 detects that there is extra trailing garbage after the compressed data
459 and emits a warning by default. You have to use the --quiet option to
460 suppress the warning. This option can be set in the
462 environment variable as in:
463 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
464 for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
466 In the above example, gzip is invoked implicitly by the -z option of
467 GNU tar. Make sure that the same block size (-b option of tar) is used
468 for reading and writing compressed data on tapes. (This example
469 assumes you are using the GNU version of tar.)
471 The --list option reports incorrect sizes if they exceed 2 gigabytes.
472 The --list option reports sizes as -1 and crc as ffffffff if the
473 compressed file is on a non seekable media.
475 In some rare cases, the --best option gives worse compression than
476 the default compression level (-6). On some highly redundant files,
478 compresses better than