--- /dev/null
+1 GZIP
+NAME
+ gzip, gunzip, zcat - compress or expand files
+
+SYNOPSIS
+ gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ... ]
+ gunzip [ -acfhlLnNrtvV ] [-S suffix] [ name ... ]
+ zcat [ -fhLV ] [ name ... ]
+
+2 DESCRIPTION
+ Gzip reduces the size of the named files using Lempel-Ziv
+ coding (LZ77). Whenever possible, each file is replaced by
+ one with the extension .gz, while keeping the same ownership
+ modes, access and modification times. (The default exten-
+ sion is -gz for VMS, 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 out-
+ put. Gzip will only attempt to compress regular files.
+
+ If the compressed file name is too long for its file system,
+ gzip truncates it. Gzip attempts to truncate only the parts
+ of the file name longer than 3 characters. (A part is del-
+ imited 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.
+
+ By default, gzip keeps the original file name and timestamp
+ in the compressed file. These are used when decompressing
+ the file with the -N option. This is useful when the
+ compressed file name was truncated or when the time stamp
+ was not preserved after a file transfer.
+
+ Compressed files can be restored to their original form
+ using gzip -d or gunzip or 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.
+
+ 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. gunzip
+ also recognizes the special extensions .tgz and .taz as
+ shorthands for .tar.gz and .tar.Z respectively. When
+ compressing, gzip uses the .tgz extension if necessary
+ instead of truncating a file with a .tar extension.
+
+ gunzip can currently decompress files created by gzip, zip,
+ compress, compress -H or pack. The detection of the input
+ format is automatic. When using the first two formats,
+ gunzip checks a 32 bit CRC. For pack, gunzip checks the
+ uncompressed length. The standard compress format was not
+ designed to allow consistency checks. However 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 uncompress does not
+ complain. This generally means that the standard uncompress
+ does not check its input, and happily generates garbage out-
+ put. The SCO compress -H format (lzh compression method)
+ does not include a CRC but also allows some consistency
+ checks.
+
+ Files created by 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 unzip instead of gunzip.
+
+ zcat is identical to gunzip -c. (On some systems, zcat may
+ be installed as gzcat to preserve the original link to
+ compress.) zcat uncompresses either a list of files on the
+ command line or its standard input and writes the
+ uncompressed data on standard output. zcat will uncompress
+ files that have the correct magic number whether they have a
+ .gz suffix or not.
+
+ Gzip uses the Lempel-Ziv algorithm used in zip and PKZIP.
+ The amount of compression obtained depends on the size of
+ the input and the distribution of common substrings. Typi-
+ cally, 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 compress), Huffman coding (as
+ used in pack), or adaptive Huffman coding (compact).
+
+ Compression is always performed, even if the compressed file
+ is slightly larger than the original. The worst case expan-
+ sion 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. gzip preserves the mode, ownership
+ and timestamps of files when compressing or decompressing.
+
+2 OPTIONS
+ -a --ascii
+ Ascii text mode: convert end-of-lines using local con-
+ ventions. 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.
+
+ -c --stdout --to-stdout
+ Write output on standard output; keep original files
+ unchanged. If there are several input files, the out-
+ put consists of a sequence of independently compressed
+ members. To obtain better compression, concatenate all
+ input files before compressing them.
+
+ -d --decompress --uncompress
+ Decompress.
+
+ -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 writ-
+ ten to a terminal. If the input data is not in a format
+ recognized by gzip, and if the option --stdout is also
+ given, copy the input data without change to the stan-
+ dard ouput: let zcat behave as cat. If -f is not given,
+ and when not running in the background, gzip prompts to
+ verify whether an existing file should be overwritten.
+
+ -h --help
+ Display a help screen and quit.
+
+ -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 on VMS because it
+ it is not possible to seek reliably to the end of the
+ compressed file, where this size is stored.
+
+ 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 on VMS for the reason given
+ above about the uncompressed size.
+
+ 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.
+
+ -L --license
+ Display the gzip license and quit.
+
+ -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 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.
+
+ -N --name
+ When compressing, always save the original file name
+ and time stamp; this is the default. When decompress-
+ ing, 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.
+
+ -q --quiet
+ Suppress all warnings.
+
+ -r --recursive
+ Travel the directory structure recursively. If any of
+ the file names specified on the command line are direc-
+ tories, gzip will descend into the directory and
+ compress all the files it finds there (or decompress
+ them in the case of gunzip ).
+
+ -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. A null suffix forces gunzip to try
+ decompression on all given files regardless of suffix,
+ as in:
+
+ gunzip --suffix "" *.*
+
+ Previous versions of gzip used the -z suffix. This was
+ changed to avoid a conflict with pack on Unix.
+
+ -t --test
+ Test. Check the compressed file integrity.
+
+ -v --verbose
+ Verbose. Display the name and percentage reduction for
+ each file compressed or decompressed.
+
+ -V --version
+ Version. Display the version number and compilation
+ options then quit.
+
+ -# --fast --best
+ Regulate the speed of compression using the specified
+ digit #, where -1 or --fast indicates the fastest
+ compression method (less compression) and -9 or --best
+ indicates the slowest compression method (best compres-
+ sion). The default compression level is -6 (that is,
+ biased towards high compression at expense of speed).
+
+2 ENVIRONMENT
+ The environment variable GZIP_OPT can hold a set of default
+ options for gzip. These options are interpreted first and
+ can be overwritten by explicit command line parameters. For
+ example:
+ define GZIP_OPT "-8 -v"
+
+2 SEE ALSO
+ compress, zip, unzip
+
+2 DIAGNOSTICS
+ Exit status is normally 0; if an error occurs, exit status
+ is 1. If a warning occurs, exit status is 2.
+
+ Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
+ Invalid options were specified on the command line.
+ file: not in gzip format
+ The file specified to gunzip has not been
+ compressed.
+ file: Corrupt input. Use zcat to recover some data.
+ The compressed file has been damaged. The data up to
+ the point of failure can be recovered using
+ define /user sys$output file.recover
+ zcat file
+ file: compressed with xx bits, can only handle yy bits
+ File was compressed (using LZW) by a program that
+ could deal with more bits than the decompress code
+ on this machine. Recompress the file with gzip,
+ which compresses better and uses less memory.
+ file: already has -gz suffix -- no change
+ The file is assumed to be already compressed.
+ Rename the file and try again.
+ file already exists; do you wish to overwrite (y or n)?
+ Respond "y" if you want the output file to be
+ replaced; "n" if not.
+ gunzip: corrupt input
+ A SIGSEGV violation was detected which usually means
+ that the input file has been corrupted.
+ xx.x%
+ Percentage of the input saved by compression.
+ (Relevant only for -v and -l.)
+ -- not a regular file or directory: ignored
+ When the input file is not a regular file or direc-
+ tory, it is left unaltered.
+
+2 CAVEATS
+ On VMS:
+ - upper case options need quotes: gzip "-V".
+ - restoration of timestamps and version numbers is not supported
+ - If a compressed file already exists, gzip -f overwrites it, it
+ does not create a new version.
+ - multi-part gzip files are not supported.
+ - gunzip does not preserve the input file format. You can use a
+ separate utility to restore the original format.
+ - gunzip and zcat can be used only if you have created the
+ links to gzip as documented in makegzip.com. Otherwise
+ you must use explicit parameters ("gzip -c" or "gzip -dc").
+ - gzip --list cannot give the uncompressed size and crc.
+
+ When writing compressed data to a tape, it is generally
+ necessary to pad the output with zeroes up to a block boun-
+ dary. When the data is read and the whole block is passed to
+ gunzip for decompression, gunzip detects that there is extra
+ trailing garbage after the compressed data and emits a warn-
+ ing by default. You have to use the --quiet option to
+ suppress the warning. This option can be set in the GZIP_OPT
+ environment variable as in:
+ define GZIP_OPT "-q"
+
+2 BUGS
+ On VMS, files in VFC record format are not correctly handled by
+ the C runtime library (the linefeed character is suppressed).
+
+ In some rare cases, the --best option gives worse compres-
+ sion than the default compression level (-6). On some highly
+ redundant files, compress compresses better than gzip.
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