+++ /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 output: 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.
projects / debian / gzip / blobdiff