gunzip -- Command

GNU utility to uncompress files
gunzip [ -cfhLrtvV ] [ file ... ]

gunzip is the GNU command that  uncompresses each file named on its command
line.

Whenever possible, gunzip replaces each file  whose name ends with .z or .Z
(and which begins with the  correct magic number) with an uncompressed file
without the original suffix.  gunzip also recognizes the special extensions
.tgz and .taz as shorthands for .tar.z or .tar.Z.

gunzip can currently decompress files created by the COHERENT commands gzip
or compress, or by the UNIX  commands zip or pack. It automatically detects
the  format  by  which the  file  is  compressed  and  applies the  correct
algorithm to uncompress it.

When uncompressing the formats used by gzip and zip, gunzip checks a 32-bit
CRC.  For files compressed by pack, gunzip checks the uncompressed length.

The format  used by compress was not designed  to allow consistency checks.
However, gunzip  can sometimes detect a  corrupted .Z file.  If  you get an
error  when uncompressing  a .Z  file, do  not assume that  the .Z  file is
correct simply  because the COHERENT command  uncompress does not complain.
This generally  means that most implementations of  uncompress do not check
their input, and happily generate garbage output.

Command-Line Options

gunzip 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.

-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.

-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.

See Also

commands,
compress,
compression,
gzip,
unpack

Diagnostics

gunzip returns zero if all went  well.  It returns one if an error occurred
and it returns two if it had to issue a warning message.

gunzip can issue the following warning messages:

file: not in gzip format
     A file named on the command line was not compressed.

     The compressed file has been  damaged.  If the data were compressed by
     the program compress, they can be  recovered up to the point of damage
     by using the program zcat to concatenate the file into another file.

file: compressed with XX bits, can only handle YY bits
     file was compressed  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
     file has  the suffix .z  or .Z; therefore,  gunzip assumes that  it is
     compressed already.

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
     gunzip  detected a  SIGSEGV violation,  which  usually means  that the
     input file has been corrupted.

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