Xdelta(1)						      General Commands Manual							 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 origi-
       nal  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 automat-
       ically  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 gen-
       eral, 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 dur-
       ing  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 (C) 1997, 1998, 1999, 2000, 2001

																	 Xdelta(1)