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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

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