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gzip(1)								       gzip(1)

       gzip, gunzip, gzcat - Compresses or expands files.

       gzip [-acdfhlLnNrtvV19] [-S suffix] [name...]

       gunzip [-acfhlLnNrtvV] [-S suffix] [name...]

       gzcat [-afhlLnNrtvV] [-S suffix] [name...]

       Specifies  ascii	 text  mode;  converts end-of-line using local conven‐
       tions. This option is supported	only  on  some	nonUnix	 systems.  For
       MSDOS,  CR  LF is converted to LF when compressing, and LF is converted
       to CR LF when decompressing.  Writes output on standard	output;	 keeps
       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

	      The gzcat command is equivalent to the gunzip  -c	 or  gzip  -cd
	      command.	Specifies an uncompress operation.

	      The  gunzip command is equivalent to the gzip -d command.	 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 the gzip command, and if the -c
	      option is also specified, copy the input data without change  to
	      the  standard  output;  that is, let the gzcat command behave as
	      the cat command. If the -f option is not specified, and when not
	      running  in  the	background, the gzip command prompts to verify
	      whether an existing file should be overwritten.  Displays a help
	      screen  and  quits.   Lists  the	following fields for each com‐
	      pressed file: Specifies size of the compressed file.   Specifies
	      size  of the uncompressed file.  Specifies compression ratio (or
	      0.0% if unknown).	 Specifies the name of the uncompressed file.

	      The uncompressed size is given as -1 for files that are  not  in
	      the gzip format, such as compressed files.

	      When used with the -v option, the following fields are also dis‐
	      played: Specifies compression method.  Specifies the 32-bit  CRC
	      of  the  uncompressed  data.   Specifies	the time stamp for the
	      uncompressed file.

	      The compression methods currently supported  are	deflate,  com‐
	      press,  lzh  (SCO compress -H) and pack.	The crc value is given
	      as ffffffff for a file that is not in the	 gzip  format.	  When
	      used  with the -N option, the uncompressed name and the date and
	      time are those stored within the compressed file, if present.

	      When used with the -v option, the size  totals  and  compression
	      ratio  for  all  files  is also displayed, unless some sizes are
	      unknown. When the -q option is specified, the title  and	totals
	      lines  are  not displayed.  Displays the gzip license and quits.
	      Specifies that the original file name and	 time  stamp  are  not
	      saved when compressing 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.	Speci‐
	      fies,  when  compressing,	 to always save the original file name
	      and  time stamp; this is the  default.  Specifies,  when	decom‐
	      pressing,	 to  restore the original file name and time stamp, if
	      present.	This option is useful on systems which have a limit on
	      the  length  of a file name or when the time stamp has been lost
	      after a file transfer.  Suppresses all  warnings.	  Travels  the
	      directory structure recursively. If any of the file names speci‐
	      fied on the command  line	 are  directories,  the	 gzip  command
	      descends	into  the  directory  and  compresses all the files it
	      finds there (or decompresses them in the case of the gunzip com‐
	      mand).   Uses  the  suffix  instead  of and should be avoided to
	      remove confusion when files are transferred to other systems.  A
	      null  suffix  forces the gunzip command to attempt decompressing
	      all given files regardless of the suffix, as follows:

	      gunzip -S	 *	 (*.* for MSDOS)

	      Previous versions of the gzip command used the suffix. This  was
	      changed  to  avoid  a conflict with the pack command.  Specifies
	      that the compressed file's integrity be tested.  Specifies  ver‐
	      bose  mode.  Displays the name and percentage reduction for each
	      file compressed or decompressed.	Specifies the  version	number
	      and  compilation options and then quits.	Regulates the speed of
	      compression by using the specified digit	#,  for	 which	-1  or
	      --fast  indicates	 the fastest compression method (less compres‐
	      sion) and -9 or --best indicates the slowest compression	method
	      (best  compression).   The default compression level is -6 (that
	      is, biased towards high compression at the expense of speed).

       The gzip command reduces the size of specified files using the  Lempel-
       Ziv  coding  (LZ77).   Whenever	possible, each file is replaced by one
       with the extension modes, access and modification times.

       If files are not specified, or if a file	 name  is  “-”,	 the  standard
       input  is  compressed  to  the standard	output.	 The gzip command only
       attempts to compress regular files.  In particular, it ignores symbolic

       By  default,  the  gzip	command	 keeps the original file name and time
       stamp 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

       Compressed  files can be restored to their original form using the gzip
       command with the -d option, or by using the gunzip command.

       The gunzip command takes a list of specified files  and	replaces  each
       file that begins with the correct magic number and whose name ends with
       -gz, -z, _z or with an uncompressed file without	 the  original	exten‐
       sion. The gunzip command also recognizes the special  extensions and as
       shorthands for and respectively.	 When compressing,  the	 gzip  command
       uses  the  extension  if	 necessary instead of truncating a file with a

       The gunzip command can currently decompress files that are  created  by
       the gzip, zip, compress, compress -H or pack commands. The detection of
       the input format is automatic. When using the first  two	 formats,  the
       gunzip  command	checks a 32-bit CRC.  For the pack command, the gunzip
       command checks the uncompressed length.	Although the standard compress
       format was not designed to allow consistency checks, the gunzip command
       is sometimes able to detect a bad file in cases	where  the  uncompress
       command	does  not. Therefore, if you get an error when uncompressing a
       file, do not assume that the file is correct if the same	 file  can  be
       decompressed  without  error  by the uncompress command.	 In this case,
       the uncompress command probably did not process	the  input  file  cor‐
       rectly, and the generated output file is not useful.

       The  gzip  command  uses	 the  Lempel-Ziv algorithm used in the zip and
       PKZIP commands.	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 the
       compress command), Huffman coding (as used in  the  pack	 command),  or
       adaptive Huffman coding (in the compact command).

       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.  The gzip command preserves
       the mode, ownership and time stamps of files when compressing or decom‐

   Advanced Usage
       Multiple compressed files can be concatenated. In this case, the gunzip
       command extracts all members at once. For example:  gzip	 -c  file1   >
       foo.gz gzip -c file2 >> foo.gz

       Using  the  previous  example, gunzip -c foo is equivalent to cat file1

       In case a member of a file is  damaged,	other  members	can  still  be
       recovered (if the damaged member is removed).  However, you gain better
       compression by compressing all members at once as  follows:  cat	 file1
       file2 | gzip > foo.gz

       The  preceding  command	line compresses better than the following one:
       gzip -c file1 file2 > foo.gz

       If you want to recompress concatenated files to	gain  better  compres‐
       sion, do the following: gzip -cd old.gz | gzip > new.gz

       If a compressed file consists of several members, the uncompressed size
       and CRC reported by the -l option applies to the last member only.   If
       you  need the uncompressed size for all members, use the following com‐
       mand: gzip -cd file.gz | wc -c

       To create a single archive file with multiple members so	 that  members
       can  later  be extracted independently, use an archiver such as the tar
       or zip commands. GNU tar supports the -z option to invoke the gzip com‐
       mand  transparently.   The  gzip command is designed as a complement to
       the tar command, not as a replacement.

       The environment variable GZIP can hold a set of default options for the
       gzip command.  These options are interpreted first and can be overwrit‐
       ten by explicit command line options as follows.

       GZIP="-8v --name"; export GZIP (for sh) setenv GZIP "-8v	 --name"  (for

       When  writing  compressed  data to a tape, it is generally necessary to
       pad the output with zeroes up to a block boundary.  When	 the  data  is
       read and the whole block is passed to the gunzip command for decompres‐
       sion, the gunzip command detects that there is extra  trailing  garbage
       after  the compressed data and emits a warning by default.  You have to
       use the -q option to suppress warnings. This option can be set  in  the
       GZIP environment variable as follows:

       GZIP="-q"   tar	-xfz  --block-compress	/dev/tape/tape0_d1   (for  sh)
       (setenv GZIP -q; tar -xfz --block-compr /dev/tape/tape0_d1 (for csh)

       In the previous example, the gzip command is invoked implicitly by  the
       -z  option  of  the GNU tar command. Make sure that the same block size
       (specified by the -b option of the tar command) is used for reading and
       writing	compressed  data on tapes.  (This example assumes that you are
       using the GNU version of the tar command.)

       The --list flag reports incorrect sizes if they exceed 2 gigabytes. The
       --list  flag  reports sizes as -1 and crc as ffffffff if the compressed
       file is on a nonseekable media.

       In rare cases, the --best flag gives worse compression than the default
       compression  level  (-6).  On some highly redundant files, the compress
       command compresses better than gzip command.

       [Tru64 UNIX]  The gzip command  may  not	 preserve  the	extended  file
       attributes  (property  list)  of	 a  file, including any access control
       lists (ACL). Verify that any ACLs are not removed or modified by	 using

       Success.	 An error occurred.  A warning is encountered.

       Commands:  compress(1), pack(1)

       Files:  acl(4)


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