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-.PU
-.TH GZIP 1 local
-.SH NAME
-gzip, gunzip, zcat \- compress or expand files
-.SH SYNOPSIS
-.ll +8
-.B gzip
-.RB [ " \-acdfhlLnNrtvV19 " ]
-.RB [ \-S\ suffix ]
-[
-.I "name \&..."
-]
-.ll -8
-.br
-.B gunzip
-.RB [ " \-acfhlLnNrtvV " ]
-.RB [ \-S\ suffix ]
-[
-.I "name \&..."
-]
-.br
-.B zcat
-.RB [ " \-fhLV " ]
-[
-.I "name \&..."
-]
-.SH DESCRIPTION
-.I Gzip
-reduces the size of the named files using Lempel-Ziv coding (LZ77).
-Whenever possible,
-each file is replaced by one with the extension
-.B "\&.gz,"
-while keeping the same ownership modes, access and modification times.
-(The default extension is
-.B "\-gz"
-for VMS,
-.B "z"
-for MSDOS, OS/2 FAT, Windows NT FAT and Atari.)
-If no files are specified, or if a file name is "-", the standard input is
-compressed to the standard output.
-.I Gzip
-will only attempt to compress regular files.
-In particular, it will ignore symbolic links.
-.PP
-If the compressed file name is too long for its file system,
-.I gzip
-truncates it.
-.I Gzip
-attempts to truncate only the parts of the file name longer than 3 characters.
-(A part is delimited by dots.) If the name consists of small parts only,
-the longest parts are truncated. For example, if file names are limited
-to 14 characters, gzip.msdos.exe is compressed to gzi.msd.exe.gz.
-Names are not truncated on systems which do not have a limit on file name
-length.
-.PP
-By default,
-.I gzip
-keeps the original file name and timestamp in the compressed file. These
-are used when decompressing the file with the
-.B \-N
-option. This is useful when the compressed file name was truncated or
-when the time stamp was not preserved after a file transfer.
-.PP
-Compressed files can be restored to their original form using
-.I gzip -d
-or
-.I gunzip
-or
-.I zcat.
-If the original name saved in the compressed file is not suitable for its
-file system, a new name is constructed from the original one to make it
-legal.
-.PP
-.I gunzip
-takes a list of files on its command line and replaces each
-file whose name ends with .gz, -gz, .z, -z, _z or .Z
-and which begins with the correct magic number with an uncompressed
-file without the original extension.
-.I gunzip
-also recognizes the special extensions
-.B "\&.tgz"
-and
-.B "\&.taz"
-as shorthands for
-.B "\&.tar.gz"
-and
-.B "\&.tar.Z"
-respectively.
-When compressing,
-.I gzip
-uses the
-.B "\&.tgz"
-extension if necessary instead of truncating a file with a
-.B "\&.tar"
-extension.
-.PP
-.I gunzip
-can currently decompress files created by
-.I gzip, zip, compress, compress -H
-or
-.I pack.
-The detection of the input format is automatic. When using
-the first two formats,
-.I gunzip
-checks a 32 bit CRC. For
-.I pack, gunzip
-checks the uncompressed length. The standard
-.I compress
-format was not designed to allow consistency checks. However
-.I gunzip
-is sometimes able to detect a bad .Z file. If you get an error
-when uncompressing a .Z file, do not assume that the .Z file is
-correct simply because the standard
-.I uncompress
-does not complain. This generally means that the standard
-.I uncompress
-does not check its input, and happily generates garbage output.
-The SCO compress -H format (lzh compression method) does not include a CRC
-but also allows some consistency checks.
-.PP
-Files created by
-.I zip
-can be uncompressed by gzip only if they have a single member compressed
-with the 'deflation' method. This feature is only intended to help
-conversion of tar.zip files to the tar.gz format. To extract zip files
-with several members, use
-.I unzip
-instead of
-.I gunzip.
-.PP
-.I zcat
-is identical to
-.I gunzip
-.B \-c.
-(On some systems,
-.I zcat
-may be installed as
-.I gzcat
-to preserve the original link to
-.I compress.)
-.I zcat
-uncompresses either a list of files on the command line or its
-standard input and writes the uncompressed data on standard output.
-.I zcat
-will uncompress files that have the correct magic number whether
-they have a
-.B "\&.gz"
-suffix or not.
-.PP
-.I Gzip
-uses the Lempel-Ziv algorithm used in
-.I zip
-and PKZIP.
-The amount of compression obtained depends on the size of the
-input and the distribution of common substrings.
-Typically, text such as source code or English
-is reduced by 60\-70%.
-Compression is generally much better than that achieved by
-LZW (as used in
-.IR compress ),
-Huffman coding (as used in
-.IR pack ),
-or adaptive Huffman coding
-.RI ( compact ).
-.PP
-Compression is always performed, even if the compressed file is
-slightly larger than the original. The worst case expansion is
-a few bytes for the gzip file header, plus 5 bytes every 32K block,
-or an expansion ratio of 0.015% for large files. Note that the actual
-number of used disk blocks almost never increases.
-.I gzip
-preserves the mode, ownership and timestamps of files when compressing
-or decompressing.
-
-.SH OPTIONS
-.TP
-.B \-a --ascii
-Ascii text mode: convert end-of-lines using local conventions. This option
-is supported only on some non-Unix systems. For MSDOS, CR LF is converted
-to LF when compressing, and LF is converted to CR LF when decompressing.
-.TP
-.B \-c --stdout --to-stdout
-Write output on standard output; keep original files unchanged.
-If there are several input files, the output consists of a sequence of
-independently compressed members. To obtain better compression,
-concatenate all input files before compressing them.
-.TP
-.B \-d --decompress --uncompress
-Decompress.
-.TP
-.B \-f --force
-Force compression or decompression even if the file has multiple links
-or the corresponding file already exists, or if the compressed data
-is read from or written to a terminal. If the input data is not in
-a format recognized by
-.I gzip,
-and if the option --stdout is also given, copy the input data without change
-to the standard ouput: let
-.I zcat
-behave as
-.I cat.
-If
-.B \-f
-is not given,
-and when not running in the background,
-.I gzip
-prompts to verify whether an existing file should be overwritten.
-.TP
-.B \-h --help
-Display a help screen and quit.
-.TP
-.B \-l --list
-For each compressed file, list the following fields:
-
- compressed size: size of the compressed file
- uncompressed size: size of the uncompressed file
- ratio: compression ratio (0.0% if unknown)
- uncompressed_name: name of the uncompressed file
-
-The uncompressed size is given as -1 for files not in gzip format,
-such as compressed .Z files. To get the uncompressed size for such a file,
-you can use:
-
- zcat file.Z | wc -c
-
-In combination with the --verbose option, the following fields are also
-displayed:
-
- method: compression method
- crc: the 32-bit CRC of the uncompressed data
- date & time: time stamp for the uncompressed file
-
-The compression methods currently supported are deflate, compress, lzh
-(SCO compress -H) and pack. The crc is given as ffffffff for a file
-not in gzip format.
-
-With --name, the uncompressed name, date and time are
-those stored within the compress file if present.
-
-With --verbose, the size totals and compression ratio for all files
-is also displayed, unless some sizes are unknown. With --quiet,
-the title and totals lines are not displayed.
-.TP
-.B \-L --license
-Display the
-.I gzip
-license and quit.
-.TP
-.B \-n --no-name
-When compressing, do not save the original file name and time stamp by
-default. (The original name is always saved if the name had to be
-truncated.) When decompressing, do not restore the original file name
-if present (remove only the
-.I gzip
-suffix from the compressed file name) and do not restore the original
-time stamp if present (copy it from the compressed file). This option
-is the default when decompressing.
-.TP
-.B \-N --name
-When compressing, always save the original file name and time stamp; this
-is the default. When decompressing, restore the original file name and
-time stamp if present. This option is useful on systems which have
-a limit on file name length or when the time stamp has been lost after
-a file transfer.
-.TP
-.B \-q --quiet
-Suppress all warnings.
-.TP
-.B \-r --recursive
-Travel the directory structure recursively. If any of the file names
-specified on the command line are directories,
-.I gzip
-will descend into the directory and compress all the files it finds there
-(or decompress them in the case of
-.I gunzip
-).
-.TP
-.B \-S .suf --suffix .suf
-Use suffix .suf instead of .gz. Any suffix can be given, but suffixes
-other than .z and .gz should be avoided to avoid confusion when files
-are transferred to other systems. A null suffix forces gunzip to try
-decompression on all given files regardless of suffix, as in:
-
- gunzip -S "" * (*.* for MSDOS)
-
-Previous versions of gzip used
-the .z suffix. This was changed to avoid a conflict with
-.IR pack "(1)".
-.TP
-.B \-t --test
-Test. Check the compressed file integrity.
-.TP
-.B \-v --verbose
-Verbose. Display the name and percentage reduction for each file compressed
-or decompressed.
-.TP
-.B \-V --version
-Version. Display the version number and compilation options then quit.
-.TP
-.B \-# --fast --best
-Regulate the speed of compression using the specified digit
-.IR # ,
-where
-.B \-1
-or
-.B \-\-fast
-indicates the fastest compression method (less compression)
-and
-.B \-9
-or
-.B \-\-best
-indicates the slowest compression method (best compression).
-The default compression level is
-.BR \-6
-(that is, biased towards high compression at expense of speed).
-.SH "ADVANCED USAGE"
-Multiple compressed files can be concatenated. In this case,
-.I gunzip
-will extract all members at once. For example:
-
- gzip -c file1 > foo.gz
- gzip -c file2 >> foo.gz
-
-Then
- gunzip -c foo
-
-is equivalent to
-
- cat file1 file2
-
-In case of damage to one member of a .gz file, other members can
-still be recovered (if the damaged member is removed). However,
-you can get better compression by compressing all members at once:
-
- cat file1 file2 | gzip > foo.gz
-
-compresses better than
-
- gzip -c file1 file2 > foo.gz
-
-If you want to recompress concatenated files to get better compression, do:
-
- gzip -cd old.gz | gzip > new.gz
-
-If a compressed file consists of several members, the uncompressed
-size and CRC reported by the --list option applies to the last member
-only. If you need the uncompressed size for all members, you can use:
-
- gzip -cd file.gz | wc -c
-
-If you wish to create a single archive file with multiple members so
-that members can later be extracted independently, use an archiver
-such as tar or zip. GNU tar supports the -z option to invoke gzip
-transparently. gzip is designed as a complement to tar, not as a
-replacement.
-.SH "ENVIRONMENT"
-The environment variable
-.B GZIP
-can hold a set of default options for
-.I gzip.
-These options are interpreted first and can be overwritten by
-explicit command line parameters. For example:
- for sh: GZIP="-8v --name"; export GZIP
- for csh: setenv GZIP "-8v --name"
- for MSDOS: set GZIP=-8v --name
-
-On Vax/VMS, the name of the environment variable is GZIP_OPT, to
-avoid a conflict with the symbol set for invocation of the program.
-.SH "SEE ALSO"
-znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1),
-pack(1), compact(1)
-.SH "DIAGNOSTICS"
-Exit status is normally 0;
-if an error occurs, exit status is 1. If a warning occurs, exit status is 2.
-.PP
-Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
-.in +8
-Invalid options were specified on the command line.
-.in -8
-.IR file :
-not in gzip format
-.in +8
-The file specified to
-.I gunzip
-has not been compressed.
-.in -8
-.IR file:
-Corrupt input. Use zcat to recover some data.
-.in +8
-The compressed file has been damaged. The data up to the point of failure
-can be recovered using
-.in +8
-zcat file > recover
-.in -16
-.IR file :
-compressed with
-.I xx
-bits, can only handle
-.I yy
-bits
-.in +8
-.I File
-was compressed (using LZW) by a program that could deal with
-more
-.I bits
-than the decompress code on this machine.
-Recompress the file with gzip, which compresses better and uses
-less memory.
-.in -8
-.IR file :
-already has .gz suffix -- no change
-.in +8
-The file is assumed to be already compressed.
-Rename the file and try again.
-.in -8
-.I file
-already exists; do you wish to overwrite (y or n)?
-.in +8
-Respond "y" if you want the output file to be replaced; "n" if not.
-.in -8
-gunzip: corrupt input
-.in +8
-A SIGSEGV violation was detected which usually means that the input file has
-been corrupted.
-.in -8
-.I "xx.x%"
-.in +8
-Percentage of the input saved by compression.
-(Relevant only for
-.BR \-v
-and
-.BR \-l \.)
-.in -8
--- not a regular file or directory: ignored
-.in +8
-When the input file is not a regular file or directory,
-(e.g. a symbolic link, socket, FIFO, device file), it is
-left unaltered.
-.in -8
--- has
-.I xx
-other links: unchanged
-.in +8
-The input file has links; it is left unchanged. See
-.IR ln "(1)"
-for more information. Use the
-.B \-f
-flag to force compression of multiply-linked files.
-.in -8
-.SH CAVEATS
-When writing compressed data to a tape, it is generally necessary to
-pad the output with zeroes up to a block boundary. When the data is
-read and the whole block is passed to
-.I gunzip
-for decompression,
-.I gunzip
-detects that there is extra trailing garbage after the compressed data
-and emits a warning by default. You have to use the --quiet option to
-suppress the warning. This option can be set in the
-.B GZIP
-environment variable as in:
- for sh: GZIP="-q" tar -xfz --block-compress /dev/rst0
- for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
-
-In the above example, gzip is invoked implicitly by the -z option of
-GNU tar. Make sure that the same block size (-b option of tar) is used
-for reading and writing compressed data on tapes. (This example
-assumes you are using the GNU version of tar.)
-.SH BUGS
-The --list option reports incorrect sizes if they exceed 2 gigabytes.
-The --list option reports sizes as -1 and crc as ffffffff if the
-compressed file is on a non seekable media.
-
-In some rare cases, the --best option gives worse compression than
-the default compression level (-6). On some highly redundant files,
-.I compress
-compresses better than
-.I gzip.