1 Info file gzip.info, produced by Makeinfo, -*- Text -*- from input
4 This file documents the the GNU `gzip' command for compressing
7 Copyright (C) 1992-1993 Jean-loup Gailly
9 Permission is granted to make and distribute verbatim copies of
10 this manual provided the copyright notice and this permission notice
11 are preserved on all copies.
13 Permission is granted to copy and distribute modified versions of
14 this manual under the conditions for verbatim copying, provided that
15 the entire resulting derived work is distributed under the terms of a
16 permission notice identical to this one.
18 Permission is granted to copy and distribute translations of this
19 manual into another language, under the above conditions for modified
20 versions, except that this permission notice may be stated in a
21 translation approved by the Foundation.
24 File: gzip.info, Node: Top, Up: (dir)
26 This file documents the `gzip' command to compress files.
30 * Copying:: How you can copy and share `gzip'.
31 * Overview:: Preliminary information.
32 * Sample:: Sample output from `gzip'.
33 * Invoking gzip:: How to run `gzip'.
34 * Advanced usage:: Concatenated files.
35 * Environment:: The `GZIP' environment variable
36 * Tapes:: Using `gzip' on tapes.
37 * Problems:: Reporting bugs.
38 * Concept Index:: Index of concepts.
41 File: gzip.info, Node: Copying, Next: Overview, Up: Top
43 GNU GENERAL PUBLIC LICENSE
44 **************************
48 Copyright (C) 1989, 1991 Free Software Foundation, Inc.
49 675 Mass Ave, Cambridge, MA 02139, USA
51 Everyone is permitted to copy and distribute verbatim copies
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57 The licenses for most software are designed to take away your
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105 TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
107 1. This License applies to any program or other work which contains
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127 source code as you receive it, in any medium, provided that you
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152 3. If the modified program normally reads commands interactively
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164 These requirements apply to the modified work as a whole. If
165 identifiable sections of that work are not derived from the
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168 do not apply to those sections when you distribute them as
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171 distribution of the whole must be on the terms of this License,
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263 would not permit royalty-free redistribution of the Program by
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288 9. If the distribution and/or use of the Program is restricted in
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298 versions of the General Public License from time to time. Such
299 new versions will be similar in spirit to the present version,
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323 WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
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344 END OF TERMS AND CONDITIONS
346 How to Apply These Terms to Your New Programs
347 =============================================
349 If you develop a new program, and you want it to be of the greatest
350 possible use to the public, the best way to achieve this is to make it
351 free software which everyone can redistribute and change under these
354 To do so, attach the following notices to the program. It is safest
355 to attach them to the start of each source file to most effectively
356 convey the exclusion of warranty; and each file should have at least
357 the "copyright" line and a pointer to where the full notice is found.
359 ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES.
360 Copyright (C) 19YY NAME OF AUTHOR
362 This program is free software; you can redistribute it and/or
363 modify it under the terms of the GNU General Public License
364 as published by the Free Software Foundation; either version 2
365 of the License, or (at your option) any later version.
367 This program is distributed in the hope that it will be useful,
368 but WITHOUT ANY WARRANTY; without even the implied warranty of
369 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
370 GNU General Public License for more details.
372 You should have received a copy of the GNU General Public License
373 along with this program; if not, write to the Free Software
374 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
376 Also add information on how to contact you by electronic and paper
379 If the program is interactive, make it output a short notice like
380 this when it starts in an interactive mode:
382 Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR
383 Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
384 type `show w'. This is free software, and you are welcome
385 to redistribute it under certain conditions; type `show c'
388 The hypothetical commands `show w' and `show c' should show the
389 appropriate parts of the General Public License. Of course, the
390 commands you use may be called something other than `show w' and `show
391 c'; they could even be mouse-clicks or menu items--whatever suits your
394 You should also get your employer (if you work as a programmer) or
395 your school, if any, to sign a "copyright disclaimer" for the program,
396 if necessary. Here is a sample; alter the names:
398 Yoyodyne, Inc., hereby disclaims all copyright
399 interest in the program `Gnomovision'
400 (which makes passes at compilers) written
403 SIGNATURE OF TY COON, 1 April 1989
404 Ty Coon, President of Vice
406 This General Public License does not permit incorporating your
407 program into proprietary programs. If your program is a subroutine
408 library, you may consider it more useful to permit linking proprietary
409 applications with the library. If this is what you want to do, use
410 the GNU Library General Public License instead of this License.
413 File: gzip.info, Node: Overview, Next: Sample, Prev: Copying, Up: Top
418 `gzip' reduces the size of the named files using Lempel-Ziv coding
419 (LZ77). Whenever possible, each file is replaced by one with the
420 extension `.gz', while keeping the same ownership modes, access and
421 modification times. (The default extension is `-gz' for VMS, `z' for
422 MSDOS, OS/2 FAT and Atari.) If no files are specified or if a file
423 name is "-", the standard input is compressed to the standard output.
424 `gzip' will only attempt to compress regular files. In particular, it
425 will ignore symbolic links.
427 If the new file name is too long for its file system, `gzip'
428 truncates it. `gzip' attempts to truncate only the parts of the file
429 name longer than 3 characters. (A part is delimited by dots.) If the
430 name consists of small parts only, the longest parts are truncated.
431 For example, if file names are limited to 14 characters, gzip.msdos.exe
432 is compressed to gzi.msd.exe.gz. Names are not truncated on systems
433 which do not have a limit on file name length.
435 By default, `gzip' keeps the original file name and timestamp in
436 the compressed file. These are used when decompressing the file with
437 the `-N' option. This is useful when the compressed file name was
438 truncated or when the time stamp was not preserved after a file
441 Compressed files can be restored to their original form using `gzip
442 -d' or `gunzip' or `zcat'. If the original name saved in the
443 compressed file is not suitable for its file system, a new name is
444 constructed from the original one to make it legal.
446 `gunzip' takes a list of files on its command line and replaces
447 each file whose name ends with `.gz', `.z', `.Z', `-gz', `-z' or `_z'
448 and which begins with the correct magic number with an uncompressed
449 file without the original extension. `gunzip' also recognizes the
450 special extensions `.tgz' and `.taz' as shorthands for `.tar.gz' and
451 `.tar.Z' respectively. When compressing, `gzip' uses the `.tgz'
452 extension if necessary instead of truncating a file with a `.tar'
455 `gunzip' can currently decompress files created by `gzip', `zip',
456 `compress' or `pack'. The detection of the input format is automatic.
457 When using the first two formats, `gunzip' checks a 32 bit CRC (cyclic
458 redundancy check). For `pack', `gunzip' checks the uncompressed
459 length. The `compress' format was not designed to allow consistency
460 checks. However `gunzip' is sometimes able to detect a bad `.Z' file.
461 If you get an error when uncompressing a `.Z' file, do not assume that
462 the `.Z' file is correct simply because the standard `uncompress' does
463 not complain. This generally means that the standard `uncompress'
464 does not check its input, and happily generates garbage output. The
465 SCO `compress -H' format (`lzh' compression method) does not include a
466 CRC but also allows some consistency checks.
468 Files created by `zip' can be uncompressed by `gzip' only if they
469 have a single member compressed with the 'deflation' method. This
470 feature is only intended to help conversion of `tar.zip' files to the
471 `tar.gz' format. To extract `zip' files with several members, use
472 `unzip' instead of `gunzip'.
474 `zcat' is identical to `gunzip -c'. `zcat' uncompresses either a
475 list of files on the command line or its standard input and writes the
476 uncompressed data on standard output. `zcat' will uncompress files
477 that have the correct magic number whether they have a `.gz' suffix or
480 `gzip' uses the Lempel-Ziv algorithm used in `zip' and PKZIP. The
481 amount of compression obtained depends on the size of the input and
482 the distribution of common substrings. Typically, text such as source
483 code or English is reduced by 60-70%. Compression is generally much
484 better than that achieved by LZW (as used in `compress'), Huffman
485 coding (as used in `pack'), or adaptive Huffman coding (`compact').
487 Compression is always performed, even if the compressed file is
488 slightly larger than the original. The worst case expansion is a few
489 bytes for the `gzip' file header, plus 5 bytes every 32K block, or an
490 expansion ratio of 0.015% for large files. Note that the actual number
491 of used disk blocks almost never increases. `gzip' preserves the mode,
492 ownership and timestamps of files when compressing or decompressing.
495 File: gzip.info, Node: Sample, Next: Invoking gzip, Prev: Overview, Up: Top
500 Here are some realistic examples of running `gzip'.
502 This is the output of the command `gzip -h':
504 gzip 1.2.4 (18 Aug 93)
505 usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
506 -c --stdout write on standard output, keep original files unchanged
507 -d --decompress decompress
508 -f --force force overwrite of output file and compress links
509 -h --help give this help
510 -l --list list compressed file contents
511 -L --license display software license
512 -n --no-name do not save or restore the original name and time stamp
513 -N --name save or restore the original name and time stamp
514 -q --quiet suppress all warnings
515 -r --recursive operate recursively on directories
516 -S .suf --suffix .suf use suffix .suf on compressed files
517 -t --test test compressed file integrity
518 -v --verbose verbose mode
519 -V --version display version number
520 -1 --fast compress faster
521 -9 --best compress better
522 file... files to (de)compress. If none given, use standard input.
524 This is the output of the command `gzip -v texinfo.tex':
526 texinfo.tex: 71.6% -- replaced with texinfo.tex.gz
528 The following command will find all `gzip' files in the current
529 directory and subdirectories, and extract them in place without
530 destroying the original:
532 find . -name '*.gz' -print | sed 's/^\(.*\)[.]gz$/gunzip < "&" > "\1"/' | sh
535 File: gzip.info, Node: Invoking gzip, Next: Advanced usage, Prev: Sample, Up: Top
540 The format for running the `gzip' program is:
544 `gzip' supports the following options:
549 Write output on standard output; keep original files unchanged.
550 If there are several input files, the output consists of a
551 sequence of independently compressed members. To obtain better
552 compression, concatenate all input files before compressing them.
561 Force compression or decompression even if the file has multiple
562 links or the corresponding file already exists, or if the
563 compressed data is read from or written to a terminal. If the
564 input data is not in a format recognized by `gzip', and if the
565 option --stdout is also given, copy the input data without change
566 to the standard ouput: let `zcat' behave as `cat'. If `-f' is not
567 given, and when not running in the background, `gzip' prompts to
568 verify whether an existing file should be overwritten.
572 Print an informative help message describing the options then
577 For each compressed file, list the following fields:
579 compressed size: size of the compressed file
580 uncompressed size: size of the uncompressed file
581 ratio: compression ratio (0.0% if unknown)
582 uncompressed_name: name of the uncompressed file
584 The uncompressed size is given as `-1' for files not in `gzip'
585 format, such as compressed `.Z' files. To get the uncompressed
586 size for such a file, you can use:
590 In combination with the --verbose option, the following fields
593 method: compression method (deflate,compress,lzh,pack)
594 crc: the 32-bit CRC of the uncompressed data
595 date & time: time stamp for the uncompressed file
597 The crc is given as ffffffff for a file not in gzip format.
599 With --verbose, the size totals and compression ratio for all
600 files is also displayed, unless some sizes are unknown. With
601 --quiet, the title and totals lines are not displayed.
605 Display the `gzip' license then quit.
609 When compressing, do not save the original file name and time
610 stamp by default. (The original name is always saved if the name
611 had to be truncated.) When decompressing, do not restore the
612 original file name if present (remove only the `gzip' suffix from
613 the compressed file name) and do not restore the original time
614 stamp if present (copy it from the compressed file). This option
615 is the default when decompressing.
619 When compressing, always save the original file name and time
620 stamp; this is the default. When decompressing, restore the
621 original file name and time stamp if present. This option is
622 useful on systems which have a limit on file name length or when
623 the time stamp has been lost after a file transfer.
627 Suppress all warning messages.
631 Travel the directory structure recursively. If any of the file
632 names specified on the command line are directories, `gzip' will
633 descend into the directory and compress all the files it finds
634 there (or decompress them in the case of `gunzip').
638 Use suffix `SUF' instead of `.gz'. Any suffix can be given, but
639 suffixes other than `.z' and `.gz' should be avoided to avoid
640 confusion when files are transferred to other systems. A null
641 suffix forces gunzip to try decompression on all given files
642 regardless of suffix, as in:
644 gunzip -S "" * (*.* for MSDOS)
646 Previous versions of gzip used the `.z' suffix. This was changed
647 to avoid a conflict with `pack'.
651 Test. Check the compressed file integrity.
655 Verbose. Display the name and percentage reduction for each file
660 Version. Display the version number and compilation options, then
666 Regulate the speed of compression using the specified digit N,
667 where `-1' or `--fast' indicates the fastest compression method
668 (less compression) and `--best' or `-9' indicates the slowest
669 compression method (optimal compression). The default
670 compression level is `-6' (that is, biased towards high
671 compression at expense of speed).
674 File: gzip.info, Node: Advanced usage, Next: Environment, Prev: Invoking gzip, Up: Top
679 Multiple compressed files can be concatenated. In this case,
680 `gunzip' will extract all members at once. If one member is damaged,
681 other members might still be recovered after removal of the damaged
682 member. Better compression can be usually obtained if all members are
683 decompressed and then recompressed in a single step.
685 This is an example of concatenating `gzip' files:
687 gzip -c file1 > foo.gz
688 gzip -c file2 >> foo.gz
698 In case of damage to one member of a `.gz' file, other members can
699 still be recovered (if the damaged member is removed). However, you
700 can get better compression by compressing all members at once:
702 cat file1 file2 | gzip > foo.gz
704 compresses better than
706 gzip -c file1 file2 > foo.gz
708 If you want to recompress concatenated files to get better
711 zcat old.gz | gzip > new.gz
713 If a compressed file consists of several members, the uncompressed
714 size and CRC reported by the `--list' option applies to the last member
715 only. If you need the uncompressed size for all members, you can use:
719 If you wish to create a single archive file with multiple members so
720 that members can later be extracted independently, use an archiver such
721 as `tar' or `zip'. GNU `tar' supports the `-z' option to invoke `gzip'
722 transparently. `gzip' is designed as a complement to `tar', not as a
726 File: gzip.info, Node: Environment, Next: Tapes, Prev: Advanced usage, Up: Top
731 The environment variable `GZIP' can hold a set of default options
732 for `gzip'. These options are interpreted first and can be
733 overwritten by explicit command line parameters. For example:
735 for sh: GZIP="-8v --name"; export GZIP
736 for csh: setenv GZIP "-8v --name"
737 for MSDOS: set GZIP=-8v --name
739 On Vax/VMS, the name of the environment variable is `GZIP_OPT', to
740 avoid a conflict with the symbol set for invocation of the program.
743 File: gzip.info, Node: Tapes, Next: Problems, Prev: Environment, Up: Top
745 Using `gzip' on tapes
746 *********************
748 When writing compressed data to a tape, it is generally necessary
749 to pad the output with zeroes up to a block boundary. When the data is
750 read and the whole block is passed to `gunzip' for decompression,
751 `gunzip' detects that there is extra trailing garbage after the
752 compressed data and emits a warning by default. You have to use the
753 `--quiet' option to suppress the warning. This option can be set in the
754 `GZIP' environment variable, as in:
756 for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
757 for csh: (setenv GZIP "-q"; tar -xfz --block-compress /dev/rst0)
759 In the above example, `gzip' is invoked implicitly by the `-z'
760 option of GNU `tar'. Make sure that the same block size (`-b' option
761 of `tar') is used for reading and writing compressed data on tapes.
762 (This example assumes you are using the GNU version of `tar'.)
765 File: gzip.info, Node: Problems, Next: Concept Index, Prev: Tapes, Up: Top
770 If you find a bug in `gzip', please send electronic mail to
771 `jloup@chorus.fr' or, if this fails, to
772 `bug-gnu-utils@prep.ai.mit.edu'. Include the version number, which
773 you can find by running `gzip -V'. Also include in your message the
774 hardware and operating system, the compiler used to compile `gzip', a
775 description of the bug behavior, and the input to `gzip' that triggered
779 File: gzip.info, Node: Concept Index, Prev: Problems, Up: Top
786 * Environment: Environment.
788 * concatenated files: Advanced usage.
789 * invoking: Invoking gzip.
790 * options: Invoking gzip.
791 * overview: Overview.
799 Node: Copying
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800 Node: Overview
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801 Node: Sample
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802 Node: Invoking gzip
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803 Node: Advanced usage
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804 Node: Environment
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806 Node: Problems
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807 Node: Concept Index
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