gzip(1) 						      General Commands Manual							   gzip(1)

NAME

       gzip, gunzip, gzcat - Compresses or expands files.

SYNOPSIS

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

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

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

OPTIONS

       Specifies  ascii text mode; converts end-of-line using local conventions. 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 origi-
       nal  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.

	      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 compressed 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 displayed: 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,  compress, 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  com-
	      pressed  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.  Specifies, when compressing, to always save the original  file  name  and   time  stamp;  this  is  the
	      default. Specifies, when decompressing, to restore the original file name and time stamp, if present.  This option is useful on sys-
	      tems 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 specified 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
	      command).  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 verbose mode. Displays the name and percentage reduction for each file com-
	      pressed 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 compression) and -9 or --best
	      indicates the slowest compression method (best compression).  The default compression level is -6 (that is, biased towards high com-
	      pression at the expense of speed).

DESCRIPTION

       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 links.

       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
       transfer.

       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 extension. 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 extension.

       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 gun-
       zip 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 uncom-
       pressing 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 correctly, 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
       decompressing.

   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 file2.

       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 compression, 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 command: 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 command transparently.  The gzip command is designed as a complement to
       the tar command, not as a replacement.

   Environment
       The environment variable GZIP can hold a set of default options for the gzip command.  These options are interpreted first and can be over-
       written by explicit command line options as follows.

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

RESTRICTIONS

       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 decompression, 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  com-
       pressed 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 com-
       press 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 gzip.

EXIT STATUS

       Success.  An error occurred.  A warning is encountered.

SEE ALSO

       Commands:  compress(1), pack(1)

       Files:  acl(4)

																	   gzip(1)