xdelta

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 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 automati-
       cally 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  recon-
       structed	 version should be recompressed after applying the patch.  In
       general, this allows Xdelta to  operate	transparently  on  gzip	 com-
       pressed 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
       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 rec-
       ommended 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	 pre-
	      vent 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)