GZIP(1) GZIP(1)
NAME
gzip, gunzip, bzip2, bunzip2, compress, uncompress, zip,
unzip - compress and expand data
SYNOPSIS
gzip [-cvnD[1-9]] [file ...]
gunzip [-ctTvD] [file ...]
bzip2 [-cvnD[1-9]] [file ...]
bunzip2 [-cvD] [file ...]
compress [ -cv ] [ file ... ]
uncompress [ -cv ] [ file ... ]
zip [-avD[1-9]] [-f zipfile] file [...]
unzip [-cistTvD] [-f zipfile] [file ...]
DESCRIPTION
Gzip encodes files with a hybrid Lempel-Ziv 1977 and Huffman
compression algorithm known as deflate. Most of the time,
the resulting file is smaller, and will never be much big-
ger. Output files are named by taking the last path element
of each file argument and appending .gz; if the resulting
name ends with .tar.gz, it is converted to .tgz instead.
Gunzip reverses the process. Its output files are named by
taking the last path element of each file argument, convert-
ing .tgz to .tar.gz, and stripping any .gz; the resulting
name must be different from the original name.
Bzip2 and bunzip2 are similar in interface to gzip and
gunzip, but use a modified Burrows-Wheeler block sorting
compression algorithm. The default suffix for output files
is .bz2, with .tar.bz2 becoming .tbz. Bunzip2 recognizes
the extension .tbz2 as a synonym for .tbz.
Compress and uncompress are similar in interface to gzip and
gunzip, but use the Lempel-Ziv-Welch compression algorithm.
The default suffix for output files is .Z. Compress is one
of the oldest widespread Unix compression programs.
Zip encodes the named files and places the results into the
archive zipfile, or the standard output if no file is given.
Unzip extracts files from an archive created by zip. If no
files are named as arguments, all of files in the archive
are extracted. A directory's name implies all recursively
contained files and subdirectories. Zip is the de facto
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GZIP(1) GZIP(1)
standard for compression on Microsoft operating systems.
None of these programs removes the original files. If the
process fails, the faulty output files are removed.
The options are:
-a Automatically creates directories as needed, needed
for zip files created by broken implementations which
omit directories.
-c Write to standard output rather than creating an out-
put file.
-i Convert all archive file names to lower case.
-s Streaming mode. Looks at the file data adjacent to
each compressed file rather than seeking in the cen-
tral file directory. This is the mode used by unzip
if no zipfile is specified. If -s is given, -T is
ignored.
-t List matching files in the archive rather than
extracting them.
-T Set the output time to that specified in the archive.
-1 .. -9
Sets the compression level. -1 is tuned for speed, -9
for minimal output size. The best compromise is -6,
the default.
-v Produce more descriptive output. With -t, adds the
uncompressed size in bytes and the modification time
to the output. Without -t, prints the names of files
on standard error as they are compressed or decom-
pressed.
-n The gzip and bzip2 file formats include a modification
timestamp which is by default set to the modification
time of the files being compressed or the current time
when the source file is read from standard input. The
-n flag overrides this behaviour and puts a timestamp
of zero instead, making the compressed output deter-
ministic.
-D Produce debugging output.
SOURCE
/sys/src/cmd/gzip
/sys/src/cmd/bzip2
/sys/src/cmd/compress
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SEE ALSO
tar(1)
"A Technique for High Performance Data Compression", Terry
A. Welch, IEEE Computer, vol. 17, no. 6 (June 1984), pp. 8-
19.
BUGS
Unzip can only extract files which are uncompressed or com-
pressed with the deflate compression scheme. Recent zip
files fall into this category. Very recent zip files may
have tables of contents that unzip cannot read. Such files
are still readable by invoking unzip with the -s option.
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