bzip2.txt

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NAME
       bzip2, bunzip2 - a block-sorting file compressor, v1.0
       bzcat - decompresses files to stdout
       bzip2recover - recovers data from damaged bzip2 files


SYNOPSIS
       bzip2 [ -cdfkqstvzVL123456789 ] [ filenames ...  ]
       bunzip2 [ -fkvsVL ] [ filenames ...  ]
       bzcat [ -s ] [ filenames ...  ]
       bzip2recover filename


DESCRIPTION
       bzip2  compresses  files  using  the Burrows-Wheeler block
       sorting text compression algorithm,  and  Huffman  coding.
       Compression  is  generally  considerably  better than that
       achieved by more conventional LZ77/LZ78-based compressors,
       and  approaches  the performance of the PPM family of sta-
       tistical compressors.

       The command-line options are deliberately very similar  to
       those of GNU gzip, but they are not identical.

       bzip2  expects  a list of file names to accompany the com-
       mand-line flags.  Each file is replaced  by  a  compressed
       version  of  itself,  with  the  name "original_name.bz2".
       Each compressed file has the same modification date,  per-
       missions, and, when possible, ownership as the correspond-
       ing original, so that these properties  can  be  correctly
       restored  at  decompression  time.   File name handling is
       naive in the sense that there is no mechanism for preserv-
       ing  original file names, permissions, ownerships or dates
       in filesystems which lack these concepts, or have  serious
       file name length restrictions, such as MS-DOS.

       bzip2  and  bunzip2 will by default not overwrite existing
       files.  If you want this to happen, specify the -f flag.

       If no file names  are  specified,  bzip2  compresses  from
       standard  input  to  standard output.  In this case, bzip2
       will decline to write compressed output to a terminal,  as
       this  would  be  entirely  incomprehensible  and therefore
       pointless.

       bunzip2 (or bzip2 -d) decompresses  all  specified  files.
       Files which were not created by bzip2 will be detected and
       ignored, and a warning issued.  bzip2  attempts  to  guess
       the  filename  for  the decompressed file from that of the
       compressed file as follows:

              filename.bz2    becomes   filename
              filename.bz     becomes   filename
              filename.tbz2   becomes   filename.tar
              filename.tbz    becomes   filename.tar
              anyothername    becomes   anyothername.out

       If the file does not end in one of the recognised endings,
       .bz2,  .bz,  .tbz2 or .tbz, bzip2 complains that it cannot
       guess the name of the original file, and uses the original
       name with .out appended.

       As  with compression, supplying no filenames causes decom-
       pression from standard input to standard output.

       bunzip2 will correctly decompress a file which is the con-
       catenation of two or more compressed files.  The result is
       the concatenation of the corresponding uncompressed files.
       Integrity testing (-t) of concatenated compressed files is
       also supported.

       You can also compress or decompress files to the  standard
       output  by giving the -c flag.  Multiple files may be com-
       pressed and decompressed like this.  The resulting outputs
       are  fed  sequentially to stdout.  Compression of multiple
       files in this manner generates a stream containing  multi-
       ple compressed file representations.  Such a stream can be
       decompressed correctly only  by  bzip2  version  0.9.0  or
       later.   Earlier  versions of bzip2 will stop after decom-
       pressing the first file in the stream.

       bzcat (or bzip2 -dc) decompresses all specified  files  to
       the standard output.

       bzip2  will  read arguments from the environment variables
       BZIP2 and BZIP, in  that  order,  and  will  process  them
       before  any  arguments  read  from the command line.  This
       gives a convenient way to supply default arguments.

       Compression is always performed, even  if  the  compressed
       file  is slightly larger than the original.  Files of less
       than about one hundred bytes tend to get larger, since the
       compression  mechanism  has  a  constant  overhead  in the
       region of 50 bytes.  Random data (including the output  of
       most  file  compressors)  is  coded at about 8.05 bits per
       byte, giving an expansion of around 0.5%.

       As a self-check for your  protection,  bzip2  uses  32-bit
       CRCs  to make sure that the decompressed version of a file
       is identical to the original.  This guards against corrup-
       tion  of  the compressed data, and against undetected bugs
       in bzip2 (hopefully very unlikely).  The chances  of  data
       corruption  going  undetected  is  microscopic,  about one
       chance in four billion for each file processed.  Be aware,
       though,  that  the  check occurs upon decompression, so it
       can only tell you that something is wrong.  It can't  help
       you  recover  the original uncompressed data.  You can use
       bzip2recover to try to recover data from damaged files.

       Return values: 0 for a normal exit,  1  for  environmental
       problems  (file not found, invalid flags, I/O errors, &c),
       2 to indicate a corrupt compressed file, 3 for an internal
       consistency error (eg, bug) which caused bzip2 to panic.


OPTIONS
       -c --stdout
              Compress or decompress to standard output.

       -d --decompress
              Force  decompression.  bzip2, bunzip2 and bzcat are
              really the same program,  and  the  decision  about
              what  actions to take is done on the basis of which
              name is used.  This flag overrides that  mechanism,
              and forces bzip2 to decompress.

       -z --compress
              The  complement  to -d: forces compression, regard-
              less of the invokation name.

       -t --test
              Check integrity of the specified file(s), but don't
              decompress  them.   This  really  performs  a trial
              decompression and throws away the result.

       -f --force
              Force overwrite of output files.   Normally,  bzip2
              will  not  overwrite  existing  output files.  Also
              forces bzip2 to break hard links to files, which it
              otherwise wouldn't do.

       -k --keep
              Keep  (don't delete) input files during compression
              or decompression.

       -s --small
              Reduce memory usage, for compression, decompression
              and  testing.   Files  are  decompressed and tested
              using a modified algorithm which only requires  2.5
              bytes  per  block byte.  This means any file can be
              decompressed in 2300k of memory,  albeit  at  about
              half the normal speed.

              During  compression,  -s  selects  a  block size of
              200k, which limits memory use to  around  the  same
              figure,  at  the expense of your compression ratio.
              In short, if your  machine  is  low  on  memory  (8
              megabytes  or  less),  use  -s for everything.  See
              MEMORY MANAGEMENT below.

       -q --quiet
              Suppress non-essential warning messages.   Messages
              pertaining  to I/O errors and other critical events
              will not be suppressed.

       -v --verbose
              Verbose mode -- show the compression ratio for each
              file  processed.   Further  -v's  increase the ver-
              bosity level, spewing out lots of information which
              is primarily of interest for diagnostic purposes.

       -L --license -V --version
              Display  the  software  version,  license terms and
              conditions.

       -1 to -9
              Set the block size to 100 k, 200 k ..  900  k  when
              compressing.   Has  no  effect  when decompressing.
              See MEMORY MANAGEMENT below.

       --     Treats all subsequent arguments as file names, even
              if they start with a dash.  This is so you can han-
              dle files with names beginning  with  a  dash,  for
              example: bzip2 -- -myfilename.

       --repetitive-fast --repetitive-best
              These  flags  are  redundant  in versions 0.9.5 and