1 GZIPNAME     gzip, gunzip, zcat - compress or expand filesSYNOPSIS     gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ... ]     gunzip [ -acfhlLnNrtvV ] [-S suffix] [ name ... ]     zcat [ -fhLV ] [ name ... ]2 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 keeping the same ownership     modes,  access  and modification times.  (The default exten-     sion 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  out-     put.   Gzip will only attempt to compress regular files.     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  del-     imited  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  consistency  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 out-     put.   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 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 correct 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.   Typi-     cally,  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 expan-     sion 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.2 OPTIONS     -a --ascii          Ascii text mode: convert end-of-lines using local  con-          ventions.  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 out-          put 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 writ-          ten 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 stan-          dard ouput: 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 on VMS because it	  it is not possible to seek reliably to the end of the          compressed file, where this size is stored.          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  on VMS for the reason given          above about the uncompressed size.	  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 decompress-          ing, 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 direc-          tories,  gzip  will  descend  into  the  directory  and          compress  all  the  files it finds there (or decompress          them in the case of gunzip ).     -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  transferred          to   other.   A  null  suffix  forces  gunzip  to   try          decompression on all given files regardless of  suffix,          as in:              gunzip --suffix "" *.*          Previous versions of gzip used the -z suffix. This  was          changed to avoid a conflict with pack on Unix.     -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.     -# --fast --best          Regulate the speed of compression using  the  specified          digit  #,  where  -1  or  --fast  indicates the fastest          compression method (less compression) and -9 or  --best          indicates the slowest compression method (best compres-          sion).  The default compression level is -6  (that  is,          biased towards high compression at expense of speed).2 ENVIRONMENT     The environment variable GZIP_OPT can hold a set of  default     options  for  gzip.  These options are interpreted first and     can be overwritten by explicit command line  parameters. For     example:           define GZIP_OPT "-8 -v"2 SEE ALSO     compress, zip, unzip2 DIAGNOSTICS     Exit status is normally 0; if an error occurs,  exit  status     is 1. If a warning occurs, exit status is 2.     Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]             Invalid options were specified on the command line.     file: not in gzip format             The  file  specified  to   gunzip   has   not   been             compressed.     file: Corrupt input. Use zcat to recover some data.             The compressed file has been damaged. The data up to             the point of failure can be recovered using                   define /user sys$output file.recover                   zcat file     file: compressed with xx bits, can only handle yy bits             File was compressed (using LZW) 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 -gz suffix -- no change             The  file  is  assumed  to  be  already  compressed.             Rename the file and try again.     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             A SIGSEGV violation was detected which usually means             that the input file has been corrupted.     xx.x%             Percentage  of  the  input  saved  by   compression.             (Relevant only for -v and -l.)     -- not a regular file or directory: ignored             When the input file is not a regular file or  direc-             tory, it is left unaltered.2 CAVEATS     On VMS:     - upper case options need quotes: gzip "-V".     - restoration of timestamps and version numbers is not supported     - If a compressed file already exists, gzip -f overwrites it, it       does not create a new version.     - multi-part gzip files are not supported.     - gunzip does not preserve the input file format. You can use a       separate utility to restore the original format.     - gunzip and zcat can be used only if you have created the       links to gzip as documented in makegzip.com.  Otherwise       you must use explicit parameters ("gzip -c" or "gzip -dc").     - gzip --list cannot give the uncompressed size and crc.     When writing compressed data to  a  tape,  it  is  generally     necessary  to pad the output with zeroes up to a block boun-     dary. When the data is read and the whole block is passed to     gunzip for decompression, gunzip detects that there is extra     trailing garbage after the compressed data and emits a warn-     ing  by  default.  You  have  to  use  the --quiet option to     suppress the warning. This option can be set in the GZIP_OPT     environment variable as in:         define GZIP_OPT "-q"2 BUGS     On VMS, files in VFC record format are not correctly handled by     the C runtime library (the linefeed character is suppressed).     In some rare cases, the --best option gives  worse  compres-     sion than the default compression level (-6). On some highly     redundant files, compress compresses better than gzip.