man gzip Command

Man page for apt-get gzip Command

Man Page for gzip in Linux

Ubuntu Man Command : man gzip

Man Gzip  Command

This tutorial shows the man page for man gzip in linux.

Open terminal with 'su' access and type the command as shown below:
man gzip

Result of the Command Execution shown below:

GZIP(1)                                                                                                                                                      GZIP(1)



NAME
gzip, gunzip, zcat compress or expand files

SYNOPSIS
gzip [ acdfhlLnNrtvV19 ] [ S suffix] [ name ... ]
gunzip [ acfhlLnNrtvV ] [ S suffix] [ name ... ]
zcat [ fhLV ] [ 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 .gz, while keep Äê
ing the same ownership modes, access and modification times. (The default extension 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 output. Gzip will only attempt to compress regular files.
In particular, it will ignore symbolic links.

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 delimited 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 con Äê
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 generally means that the standard uncompress does not check its input, and happily
generates garbage output. 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 a zip file with a single member, use a command like gunzip <foo.zip or gunzip S .zip
foo.zip. 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 cor Äê
rect 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. Typically, 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 expansion 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.

The gzip file format is specified in P. Deutsch, GZIP file format specification version 4.3, <ftp://ftp.isi.edu/in notes/rfc1952.txt>, Internet RFC 1952 (May
1996). The zip deflation format is specified in P. Deutsch, DEFLATE Compressed Data Format Specification version 1.3, <ftp://ftp.isi.edu/in
notes/rfc1951.txt>, Internet RFC 1951 (May 1996).


OPTIONS
a ascii
Ascii text mode: convert end of lines using local conventions. 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 output 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 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.

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 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
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 for a file not in
gzip format.

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 decompressing, 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 directories, gzip will descend into the direc Äê
tory and compress all the files it finds there (or decompress them in the case of gunzip ).

rsyncable
While compressing, synchronize the output occasionally based on the input. This increases size by less than 1 percent most cases, but means that the
rsync(1) program can much more efficiently synchronize files compressed with this flag. gunzip cannot tell the difference between a compressed file
created with this option, and one created without it.

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 trans Äê
ferred 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(1).

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.


Related Topics

Apt Get Commands