IRIX Base Documentation 2001 May/SGI IRIX Base Documentation 2001 May.iso/usr/share/catman/u_man/cat1/gzip.z/gzip

Text File | 1998-10-20 | 19.6 KB | 463 lines

GGGGZZZZIIIIPPPP((((1111))))                                                                GGGGZZZZIIIIPPPP((((1111))))



NNNNAAAAMMMMEEEE
     gzip, gunzip, gzcat - compress or expand files

SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
     ggggzzzziiiipppp [ ----aaaaccccddddffffhhhhllllLLLLnnnnNNNNrrrrttttvvvvVVVV11119999 ] [----SSSS ssssuuuuffffffffiiiixxxx] [ _n_a_m_e ... ]
     gggguuuunnnnzzzziiiipppp [ ----aaaaccccffffhhhhllllLLLLnnnnNNNNrrrrttttvvvvVVVV ] [----SSSS ssssuuuuffffffffiiiixxxx] [ _n_a_m_e ... ]
     ggggzzzzccccaaaatttt [ ----ffffhhhhLLLLVVVV ] [ _n_a_m_e ... ]

DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     _G_z_i_p reduces the size of the named files using Lempel-Ziv coding (LZ77).
     Whenever possible, each file is replaced by one with the extension ....ggggzzzz,,,,
     while keeping the same ownership modes, access and modification times.
     (The default extension is ----ggggzzzz for VMS, zzzz 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 output.  _G_z_i_p will only
     attempt to compress regular files.  In particular, it will ignore
     symbolic links.

     If the compressed file name is too long for its file system, _g_z_i_p
     truncates it.  _G_z_i_p attempts to truncate only the parts of the file name
     longer than 3 characters.  (A part is delimited 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, _g_z_i_p keeps the original file name and timestamp in the
     compressed file. These are used when decompressing the file with the ----NNNN
     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 _g_z_i_p -_d or
     _g_u_n_z_i_p or _g_z_c_a_t. 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.

     _g_u_n_z_i_p 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.  _g_u_n_z_i_p also recognizes the special extensions ....ttttggggzzzz and ....ttttaaaazzzz
     as shorthands for ....ttttaaaarrrr....ggggzzzz and ....ttttaaaarrrr....ZZZZ respectively.  When compressing,
     _g_z_i_p uses the ....ttttggggzzzz extension if necessary instead of truncating a file
     with a ....ttttaaaarrrr extension.

     _g_u_n_z_i_p can currently decompress files created by _g_z_i_p, _z_i_p, _c_o_m_p_r_e_s_s,
     _c_o_m_p_r_e_s_s -_H or _p_a_c_k. The detection of the input format is automatic.
     When using the first two formats, _g_u_n_z_i_p checks a 32 bit CRC. For _p_a_c_k,
     _g_u_n_z_i_p checks the uncompressed length. The standard _c_o_m_p_r_e_s_s format was
     not designed to allow consistency checks. However _g_u_n_z_i_p 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 _u_n_c_o_m_p_r_e_s_s does not complain. This generally means that the



                                                                        PPPPaaaaggggeeee 1111






GGGGZZZZIIIIPPPP((((1111))))                                                                GGGGZZZZIIIIPPPP((((1111))))



     standard _u_n_c_o_m_p_r_e_s_s does not check its input, and happily generates
     garbage output.  The SCO compress -H format (lzh compression method) does
     not include a CRC but also allows some consistency checks.

     Files created by _z_i_p 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 _u_n_z_i_p instead of _g_u_n_z_i_p.

     _g_z_c_a_t is identical to _g_u_n_z_i_p ----cccc.... (On some systems, _z_c_a_t may be installed
     as _g_z_c_a_t to preserve the original link to _c_o_m_p_r_e_s_s.) _g_z_c_a_t uncompresses
     either a list of files on the command line or its standard input and
     writes the uncompressed data on standard output.  _g_z_c_a_t will uncompress
     files that have the correct magic number whether they have a ....ggggzzzz suffix
     or not.

     _G_z_i_p uses the Lempel-Ziv algorithm used in _z_i_p and PKZIP.  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 _c_o_m_p_r_e_s_s), Huffman coding (as used
     in _p_a_c_k), or adaptive Huffman coding (_c_o_m_p_a_c_t).

     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.  _g_z_i_p preserves the mode, ownership and
     timestamps of files when compressing or decompressing.


OOOOPPPPTTTTIIIIOOOONNNNSSSS
     ----aaaa --------aaaasssscccciiiiiiii
          Ascii text mode: convert end-of-lines using local conventions. 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.

     ----cccc --------ssssttttddddoooouuuutttt --------ttttoooo----ssssttttddddoooouuuutttt
          Write output on standard output; keep 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 them.

     ----dddd --------ddddeeeeccccoooommmmpppprrrreeeessssssss --------uuuunnnnccccoooommmmpppprrrreeeessssssss
          Decompress.

     ----ffff --------ffffoooorrrrcccceeee
          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 _g_z_i_p, and if the option --stdout is also



                                                                        PPPPaaaaggggeeee 2222






GGGGZZZZIIIIPPPP((((1111))))                                                                GGGGZZZZIIIIPPPP((((1111))))



          given, copy the input data without change to the standard ouput: let
          _g_z_c_a_t behave as _c_a_t. If ----ffff is not given, and when not running in the
          background, _g_z_i_p prompts to verify whether an existing file should
          be overwritten.

     ----hhhh --------hhhheeeellllpppp
          Display a help screen and quit.

     ----llll --------lllliiiisssstttt
          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 for files not in gzip format,
          such as compressed .Z files. To get the uncompressed size for such a
          file, you can use:

              gzcat file.Z | wc -c

          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 for a
          file not in gzip format.

          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.

     ----LLLL --------lllliiiicccceeeennnnsssseeee
          Display the _g_z_i_p license and quit.

     ----nnnn --------nnnnoooo----nnnnaaaammmmeeee
          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 _g_z_i_p 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.




                                                                        PPPPaaaaggggeeee 3333






GGGGZZZZIIIIPPPP((((1111))))                                                                GGGGZZZZIIIIPPPP((((1111))))



     ----NNNN --------nnnnaaaammmmeeee
          When compressing, always save the original file name and time stamp;
          this is the default. When decompressing, 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.

     ----qqqq --------qqqquuuuiiiieeeetttt
          Suppress all warnings.

     ----rrrr --------rrrreeeeccccuuuurrrrssssiiiivvvveeee
          Travel the directory structure recursively. If any of the file names
          specified on the command line are directories, _g_z_i_p will descend
          into the directory and compress all the files it finds there (or
          decompress them in the case of _g_u_n_z_i_p ).

     ----SSSS ....ssssuuuuffff --------ssssuuuuffffffffiiiixxxx ....ssssuuuuffff
          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 systems.  A null suffix forces
          gunzip to  try decompression on all given files regardless of
          suffix, as in:

              gunzip -S "" *       (*.* for MSDOS)

          Previous versions of gzip used the .z suffix. This was changed to
          avoid a conflict with _p_a_c_k(1).

     ----tttt --------tttteeeesssstttt
          Test. Check the compressed file integrity.

     ----vvvv --------vvvveeeerrrrbbbboooosssseeee
          Verbose. Display the name and percentage reduction for each file
          compressed or decompressed.

     ----VVVV --------vvvveeeerrrrssssiiiioooonnnn
          Version. Display the version number and compilation options then
          quit.

     ----#### --------ffffaaaasssstttt --------bbbbeeeesssstttt
          Regulate the speed of compression using the specified digit #, where
          ----1111 or --------ffffaaaasssstttt indicates the fastest compression method (less
          compression) and ----9999 or --------bbbbeeeesssstttt indicates the slowest compression
          method (best compression).  The default compression level is ----6666
          (that is, biased towards high compression at expense of speed).

AAAADDDDVVVVAAAANNNNCCCCEEEEDDDD UUUUSSSSAAAAGGGGEEEE
     Multiple compressed files can be concatenated. In this case, _g_u_n_z_i_p will
     extract all members at once. For example:

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



                                                                        PPPPaaaaggggeeee 4444






GGGGZZZZIIIIPPPP((((1111))))                                                                GGGGZZZZIIIIPPPP((((1111))))



     Then
           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,
     do:

           gzip -cd old.gz | gzip > new.gz

     If a compressed file consists of several members, the uncompressed size
     and CRC reported by the --list option applies to the last member only. If
     you need the uncompressed size for all members, you can use:

           gzip -cd file.gz | wc -c

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

EEEENNNNVVVVIIIIRRRROOOONNNNMMMMEEEENNNNTTTT
     The environment variable GGGGZZZZIIIIPPPP can hold a set of default options for _g_z_i_p.
     These options are interpreted first and can be overwritten by explicit
     command line parameters. For example:
           for sh:    GZIP="-8v --name"; export GZIP
           for csh:   setenv GZIP "-8v --name"
           for MSDOS: set GZIP=-8v --name

     On Vax/VMS, the name of the environment variable is GZIP_OPT, to avoid a
     conflict with the symbol set for invocation of the program.

SSSSEEEEEEEE AAAALLLLSSSSOOOO
     compress(1), pack(1)

DDDDIIIIAAAAGGGGNNNNOOOOSSSSTTTTIIIICCCCSSSS
     Exit status is normally 0; if an error occurs, exit status is 1. If a
     warning occurs, exit status is 2.





                                                                        PPPPaaaaggggeeee 5555






GGGGZZZZIIIIPPPP((((1111))))                                                                GGGGZZZZIIIIPPPP((((1111))))



     Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
             Invalid options were specified on the command line.
     _f_i_l_e:  not in gzip format
             The file specified to _g_u_n_z_i_p has not been compressed.
     _f_i_l_e:  Corrupt input. Use gzcat to recover some data.
             The compressed file has been damaged. The data up to the point of
             failure can be recovered using
                     gzcat file > recover
     _f_i_l_e:  compressed with _x_x bits, can only handle _y_y bits
             _F_i_l_e was compressed (using LZW) by a program that could deal with
             more _b_i_t_s than the decompress code on this machine.  Recompress
             the file with gzip, which compresses better and uses less memory.
     _f_i_l_e:  already has .gz suffix -- no change
             The file is assumed to be already compressed.  Rename the file
             and try again.
     _f_i_l_e 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.
     _x_x._x%
             Percentage of the input saved by compression.  (Relevant only for
             ----vvvv and ----llll.)
     -- not a regular file or directory: ignored
             When the input file is not a regular file or directory, (e.g. a
             symbolic link, socket, FIFO, device file), it is left unaltered.
     -- has _x_x other links: unchanged
             The input file has links; it is left unchanged.  See _l_n(1) for
             more information. Use the ----ffff flag to force compression of
             multiply-linked files.

CCCCAAAAVVVVEEEEAAAATTTTSSSS
     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 _g_u_n_z_i_p for decompression, _g_u_n_z_i_p detects
     that there is extra trailing garbage after the compressed data and emits
     a warning by default. You have to use the --quiet option to suppress the
     warning. This option can be set in the GGGGZZZZIIIIPPPP environment variable as in:
       for sh:  GZIP="-q"  tar -xfz --block-compress /dev/rst0
       for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0

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

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




                                                                        PPPPaaaaggggeeee 6666






GGGGZZZZIIIIPPPP((((1111))))                                                                GGGGZZZZIIIIPPPP((((1111))))



     In some rare cases, the --best option gives worse compression than the
     default compression level (-6). On some highly redundant files, _c_o_m_p_r_e_s_s
     compresses better than _g_z_i_p.




















































                                                                        PPPPaaaaggggeeee 7777