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Xdelta(1)                                               Xdelta(1)

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.

       -m=SIZE, --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: 1.2; Release Date: Mon, 11 Jun 2001 03:39:53 -0700.
       Copyright  1997, 1998, 1999, 2000, 2001