215 lines
8.8 KiB
Plaintext
215 lines
8.8 KiB
Plaintext
|
|
||
|
|
GZIP(1) USER COMMANDS GZIP(1)
|
||
|
|
|
||
|
|
NAME
|
||
|
|
gzip, gunzip, zcat - compress or expand files
|
||
|
|
|
||
|
|
SYNOPSIS
|
||
|
|
gzip [ -cdfhLrtvV19 ] [ name ... ]
|
||
|
|
gunzip [ -cfhLrtvV ] [ name ... ]
|
||
|
|
zcat [ -hLV ] [ name ... ]
|
||
|
|
|
||
|
|
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 .z, while keeping the same ownership
|
||
|
|
modes, access and modification times. (The extension is -z
|
||
|
|
for VMS, z for MSDOS, OS/2 and Atari.) If no files are
|
||
|
|
specified, the standard input is compressed to the standard
|
||
|
|
output. If the new file name is too long, gzip truncates it
|
||
|
|
and keeps the original file name in the compressed file.
|
||
|
|
Gzip will only attempt to compress regular files. In par-
|
||
|
|
ticular, it will ignore symbolic links.
|
||
|
|
|
||
|
|
Compressed files can be restored to their original form
|
||
|
|
using gzip -d or gunzip or zcat.
|
||
|
|
|
||
|
|
gunzip takes a list of files on its command line and
|
||
|
|
replaces each file whose name ends with .z or .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.z or .tar.Z
|
||
|
|
|
||
|
|
gunzip can currently decompress files created by gzip, zip,
|
||
|
|
compress 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 compress format was not designed to allow con-
|
||
|
|
sistency 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 gen-
|
||
|
|
erally means that the standard uncompress does not check its
|
||
|
|
input, and happily generates garbage output.
|
||
|
|
|
||
|
|
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.z 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
|
||
|
|
.z 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. gzip preserves the mode, ownership and timestamps of
|
||
|
|
files when compressing or decompressing.
|
||
|
|
|
||
|
|
OPTIONS
|
||
|
|
-c --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
|
||
|
|
Decompress.
|
||
|
|
|
||
|
|
-f --force
|
||
|
|
Force compression or decompression even if the file has
|
||
|
|
multiple links or the corresponding file already
|
||
|
|
exists. 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.
|
||
|
|
|
||
|
|
-L --license
|
||
|
|
Display the gzip license.
|
||
|
|
|
||
|
|
-q --quiet
|
||
|
|
Suppress all warnings.
|
||
|
|
|
||
|
|
-r --recurse
|
||
|
|
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 ).
|
||
|
|
|
||
|
|
-t --test
|
||
|
|
Test. Check the compressed file integrity.
|
||
|
|
|
||
|
|
-v --verbose
|
||
|
|
Verbose. Display the name and percentage reduction for
|
||
|
|
each file compressed.
|
||
|
|
|
||
|
|
-V --version
|
||
|
|
Version. Display the version number and compilation
|
||
|
|
options.
|
||
|
|
|
||
|
|
-# --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 (optimal
|
||
|
|
compression). The default compression level is -5.
|
||
|
|
|
||
|
|
ADVANCED USAGE
|
||
|
|
Multiple compressed files can be concatenated. In this case,
|
||
|
|
gunzip will extract all members at once. For example:
|
||
|
|
|
||
|
|
gzip -c file1 > foo.z
|
||
|
|
gzip -c file2 >> foo.z Then
|
||
|
|
gunzip -c foo
|
||
|
|
|
||
|
|
is equivalent to
|
||
|
|
|
||
|
|
cat file1 file2
|
||
|
|
|
||
|
|
In case of damage to one member of a .z 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.z
|
||
|
|
|
||
|
|
compresses better than
|
||
|
|
|
||
|
|
gzip -c file1 file2 > foo.z
|
||
|
|
|
||
|
|
If you want to recompress concatenated files to get better
|
||
|
|
compression, do:
|
||
|
|
|
||
|
|
zcat old.z | gzip > new.z
|
||
|
|
|
||
|
|
ENVIRONMENT
|
||
|
|
The environment variable GZIP 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:
|
||
|
|
for sh: GZIP="-8 -v"; export GZIP
|
||
|
|
for csh: setenv GZIP "-8 -v"
|
||
|
|
for MSDOS: set GZIP=-8 -v
|
||
|
|
|
||
|
|
On Vax/VMS, the name of the environment variable is
|
||
|
|
GZIP_OPT, to avoid a conflict with the symbol set for invo-
|
||
|
|
cation of the program.
|
||
|
|
|
||
|
|
SEE ALSO
|
||
|
|
znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1),
|
||
|
|
unzip(1), compress(1), pack(1), compact(1)
|
||
|
|
|
||
|
|
DIAGNOSTICS
|
||
|
|
Exit status is normally 0; if an error occurs, exit status
|
||
|
|
is 1. If a warning occurs, exit status is 2.
|
||
|
|
|
||
|
|
Usage: gzip [-cdfhLrtvV19] [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
|
||
|
|
zcat file > recover
|
||
|
|
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 z suffix -- no change
|
||
|
|
The file is assumed to be already compressed.
|
||
|
|
Rename the file and try again or use zcat.
|
||
|
|
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.)
|
||
|
|
-- not a regular file or directory: ignored
|
||
|
|
When the input file is not a regular file or direc-
|
||
|
|
tory, (e.g. a symbolic link, socket, FIFO, device
|
||
|
|
file), it is left unaltered.
|
||
|
|
-- has xx other links: unchanged
|
||
|
|
The input file has links; it is left unchanged. See
|
||
|
|
ln(1) for more information. Use the -f flag to force
|
||
|
|
compression of multiply-linked files.
|
||
|
|
|
||
|
|
CAVEATS
|
||
|
|
The .z extension is already used by pack(1). You can link
|
||
|
|
gzip to pcat to get transparent decompression for programs
|
||
|
|
expecting .z files to be in pack format.
|