gzip -- Command

GNU utility to compress files
gzip [ -cdfhLrtvV19 ] [ file ... ]

The  command gzip  is the  GNU command  that compresses  file named  on its
command line.  It will only attempt to compress regular files.

Whenever possible,  gzip replaces  each file with  one that has  the suffix
.gz,  while preserving  its ownership  and  times of  last access  and last
modification.   If the  name of  file is longer  than 12  characters (which
prevents gzip  from attaching the suffix .gz), gzip  truncates it and keeps
its original name within the compressed file.

If its command line names no  file, gzip compresses what it reads from from
the standard input, and writes it to the standard output.

To restore a compressed file, filter it thorugh the command gunzip.

gzip  uses the  Lempel-Ziv algorithm  to  perform compression.   Under most
circumstances, this  algorithm compresses files  more tightly than  do most
other commonly used techniques,  such as the LZW algorithm, Huffman coding,
or  adaptive Huffman  coding.  The amount  of compression  obtained depends
upon the  size of the input  and the distribution of  common substrings; in
general, it reduces text by 60% to 70%.

gzip always  compresses its input, 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 five bytes for every 32-kilobyte block.

Command-Line Options

gzip recognizes the following command-line options:

-c   Write output to standard output,  and do not change the original file.
     If  the command  line names  more than  one file,  gzip writes  to the
     standard output  a sequence  of independently compressed  members.  To
     obtain  better compression, concatenate  the files  before compressing
     them.

-d   Decompress each file.

-f   force compression or decompression, even if file has multiple links or
     the corresponding file  already exists.  Without this option, and when
     not  running in  the  background, gzip  prompts to  verify whether  it
     should overwrite an existing file.

-h   Help: display a screenful of information on how to run this program.

-L   Display the gzip license.

-q   Suppress all warning messages.

-r   Recurse: if  a file is  a directory, compress or  uncompress all files
     within it.

-t   Test: check the integrity of a compressed file.

-v   Verbose: display the name and percentage reduction for each file as it
     is compressed.

-V   Display the version  of this command, and the options  by which it was
     compiled.

1-9  Regulate  the speed  of compression,  on  a scale  of from  1 to  9. 1
     performs  the  fastest but  most  superficial  compression, whereas  9
     performs  the  slowest  but most  thorough  compression.   -fast is  a
     synonym  for  -1, whereas  -best  is  a synonym  for  -9. The  default
     compression level is -5.

Advanced Usage

You  can  concatenate  multiple compressed  files.   In  this case,  gunzip
extracts all members at once.  For example:

    gzip -c file1 > foo.gz
    gzip -c file2 >> foo.gz
    gunzip -c foo

is equivalent to:

    cat file1 file2

In case of  damage to one member of a  .gz 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.gz

compresses better than:

    gzip -c file1 file2 > foo.gz

If you  want to  recompress concatenated  files to get  better compression,
type:

    zcat old.gz | gzip > new.gz

Environment

gzip  reads the  environment  variable GZIP  for its  default options.   It
interprets  these options  first; you  can override  them by  setting other
options on the gzip command line.

See Also

commands,
compress,
compression,
gunzip,
uncompress,
unpack,
zcmp,
zdiff,
zforce,
zgrep,
zmore,
znew

Diagnostics

If all went well, gzip returns zero upon exiting.  If an error occurred, it
returns one; if it issued a warning message, it returns two.

gzip can issue the following warning messages:

Usage: gzip [-cdfhLrtvV19] [file ...]
     The  gzip  command  line  contained  an  option  that  gzip  does  not
     recognize.

file: already has z suffix -- no change
     file  already has  the  suffix .gz;  therefore, gzip  assumes that  it
     already is compressed.

file not a regular file or directory: ignored
     A file is  not a regular file or directory.   gzip does not attempt to
     compress devices, pipes, or other special files.

file  has XX other links: unchanged
     file has  more than one  link.  By default,  gzip does not  compress a
     file that has multiple links.

Notes

gzip is  released under  the conditions  of the Free  Software Foundation's
``copyleft''.   Full source  code is  available  through the  Mark Williams
bulletin board.

© 2012 by Stephen A. Ness