NAME

       xdelta - Invoke Xdelta

SYNOPSIS

       xdelta subcommand [ option...  ] [ operand...  ]

DESCRIPTION

       Xdelta  provides  the  ability  to generate deltas between a pair of files and later apply
       those deltas.  It operates similar to the diff and patch commands,  but  works  on  binary
       files and does not produce a human readable output.

       Xdelta has three subcommands, delta, patch, and info.  Delta accepts two file versions and
       produces a delta, while patch accepts the original file version and delta and produces the
       second  version.   The  info  command  prints  useful  information  about  a  delta.  Each
       subcommand will be detailed seperately.

   Gzip processing
       Attempting to compute a delta between compressed  input  files  usually  results  in  poor
       compression.   This  is  because  small  differences  between the original contents causes
       changes in the compression of whole blocks of data.  To simplify things, Xdelta implements
       a special case for gzip(1) compressed files.  If any version input to the delta command is
       recognized as having gzip compression,  it  will  be  automatically  decompressed  into  a
       temporary  location  prior  to comparison.  This temporary location is either the value of
       the TMPDIR environment variable, if set, otherwise "/tmp".

       The Xdelta patch header contains a flag indicating that the reconstructed  version  should
       be  recompressed  after  applying  the  patch.   In general, this allows Xdelta to operate
       transparently on gzip compressed inputs.

       There is one potential problem when automatically processing gzip compressed files,  which
       is  that  the  recompressed  content does not always match byte-for-byte with the original
       compressed content.  The uncompressed content still matches, but if there is  an  external
       integrity  check  such  as  cryptographic signature verification, it may fail.  To prevent
       this from happening, the --pristine option disables automatic gzip processing.

   MD5 integrity check
       By default, Xdelta always verifies the MD5 checksum of the files  it  reconstructs.   This
       prevents you from supplying an incorrect input during patch, which would result in corrupt
       output.  Because of this feature, you can feel confident that  patch  has  produced  valid
       results.   The  --noverify  option disables MD5 verification, but this is only recommended
       for performance testing.

   Compressed patch format
       Xdelta uses a fairly simple encoding for its delta, then applies zlib compression  to  the
       result.  You should not have to post-compress an Xdelta delta.

   Delta
       The delta subcommand has the following synopsis:

       xdelta delta [ option...  ] fromfile tofile patchout

       Computes a delta from fromfile to tofile and writes it to patchout

   Patch
       The patch subcommand has the following synopsis:

       xdelta patch [ option...  ] patchin [ fromfile [ tofile ]]

       Applies patchin to fromfile and produces a reconstructed version of tofile.

       If  fromfile  was  omitted,  Xdelta  attempts  to use the original fromfile name, which is
       stored in the delta.  The from file must be identical to the one used to create the delta.
       If its length or MD5 checksum differs, patch will abort with an error message.

       If  tofile  was  omitted,  Xdelta  attempts to use the original tofile name, which is also
       stored in the delta.  If the original  tofile  name  already  exists,  a  unique  filename
       extension will be added to avoid destroying any existing data.

   Info
       The info subcommand has the following synopsis:

       xdelta info patchinfo

       Prints  information about patchinfo and the version it reconstructs, including file names,
       lengths, and MD5 checksums.

   Options
       -0..9  Set the zlib compression level.  Zero indicates  no  compression.   Nine  indicates
              maximum compression.

       -h, --help
              Print a short help message and exit.

       -q, --quiet
              Quiet.  Surpresses several warning messages.

       -v, --version
              Print the Xdelta version number and exit.

       -V, --verbose
              Verbose.  Prints a bit of extra information.

       -n, --noverify
              No verify.  Turns off MD5 checksum verification of the input and output files.

       -mSIZE, --maxmem=SIZE
              Set  an  upper  bound  on  the  size  of  an  in-memory  page  cache.  For example,
              --maxmem=32M will use a 32 megabyte page cache.

       -s=BLOCK_SIZE
              Set the block size, unless it was hard coded (20% speed improvement).  Should be  a
              power of 2.

       -p, --pristine
              Disable  the  automatic  decompression  of  gzipped  inputs,  to prevent unexpected
              differences in the re-compressed content.

IDENTIFICATION

       Author: Joshua P. MacDonald, jmacd@cs.berkeley.edu
       Manual Page Revision: 1.5; Release Date: Fri, 29 Jun 2001 06:01:08 -0700.
       Copyright © 1997, 1998, 1999, 2000, 2001

                                                                                        Xdelta(1)