gzip: Invoking gzip
3 Invoking ‘gzip’
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The format for running the ‘gzip’ program is:
gzip OPTION ...
‘gzip’ supports the following options:
‘--stdout’
‘--to-stdout’
‘-c’
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.
‘--decompress’
‘--uncompress’
‘-d’
Decompress.
‘--force’
‘-f’
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 ‘gzip’, and if the
option ‘--stdout’ is also given, copy the input data without change
to the standard 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.
‘--help’
‘-h’
Print an informative help message describing the options then quit.
‘--keep’
‘-k’
Keep (don’t delete) input files during compression or
decompression.
‘--list’
‘-l’
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 (deflate,compress,lzh,pack)
crc: the 32-bit CRC of the uncompressed data
date & time: timestamp for the uncompressed file
The CRC is given as ffffffff for a file not in gzip format.
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.
The ‘gzip’ format represents the input size modulo 2^32, so the
uncompressed size and compression ratio are listed incorrectly for
uncompressed files 4 GiB and larger. To work around this problem,
you can use the following command to discover a large uncompressed
file’s true size:
zcat file.gz | wc -c
‘--license’
‘-L’
Display the ‘gzip’ license then quit.
‘--no-name’
‘-n’
When compressing, do not save the original file name and timestamp
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 timestamp if
present (copy it from the compressed file). This option is the
default when decompressing.
‘--name’
‘-N’
When compressing, always save the original file name, and save the
original timestamp if the original is a regular file; this is the
default. When decompressing, restore the original file name and
timestamp if present. This option is useful on systems which have
a limit on file name length or when the timestamp has been lost
after a file transfer.
‘--quiet’
‘-q’
Suppress all warning messages.
‘--recursive’
‘-r’
Travel the directory structure recursively. If any of the file
names specified on the command line are directories, ‘gzip’ will
descend into the directory and compress all the files it finds
there (or decompress them in the case of ‘gunzip’).
‘--rsyncable’
Cater better to the ‘rsync’ program by periodically resetting the
internal structure of the compressed data stream. This lets the
‘rsync’ program take advantage of similarities in the uncompressed
input when synchronizing two files compressed with this flag. The
cost: the compressed output is usually about one percent larger.
‘--suffix SUF’
‘-S 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 ‘pack’.
‘--synchronous’
Use synchronous output, by transferring output data to the output
file’s storage device when the file system supports this. Because
file system data can be cached, without this option if the system
crashes around the time a command like ‘gzip FOO’ is run the user
might lose both ‘FOO’ and ‘FOO.gz’; this is the default with
‘gzip’, just as it is the default with most applications that move
data. When this option is used, ‘gzip’ is safer but can be
considerably slower.
‘--test’
‘-t’
Test. Check the compressed file integrity.
‘--verbose’
‘-v’
Verbose. Display the name and percentage reduction for each file
compressed.
‘--version’
‘-V’
Version. Display the version number and compilation options, then
quit.
‘--fast’
‘--best’
‘-N’
Regulate the speed of compression using the specified digit N,
where ‘-1’ or ‘--fast’ indicates the fastest compression method
(less compression) and ‘--best’ or ‘-9’ indicates the slowest
compression method (optimal compression). The default compression
level is ‘-6’ (that is, biased towards high compression at expense
of speed).
Info Catalog
gzip: Sample
gzip: Top
gzip: Advanced usage