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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 automatically	decom-
       pressed 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	recon-
       structed	 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 com-
       pressed files, which is that the	recompressed content does  not	always
       match  byte-for-byte  with the original compressed content.  The	uncom-
       pressed 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 re-
       constructs.  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	recom-
       mended 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 dif-
       fers, 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, in-
       cluding 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 improve-
	      ment).  Should be	a power	of 2.

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

RETURN VALUES
       The  delta  command exits with status 0 to indicate that	no differences
       were found, with	status 1 to indicate that some differences were	found,
       and  with  status  2  to	indicate an error of some kind.	 The patch and
       info commands exit with status 0	on success and 2 on failure.

IDENTIFICATION
       Author: Joshua P. MacDonald, jmacd@cs.berkeley.edu
       Manual Page Revision: 1.6; Release Date:	 Sun,  28  Jan	2007  12:21:11
       -0800.
       Copyright (C) 1997, 1998, 1999, 2000, 2001

								     Xdelta(1)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | IDENTIFICATION

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