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RedHat 9 (Linux i386) - man page for xdelta (redhat section 1)

Xdelta(1)			     General Commands Manual				Xdelta(1)

       xdelta - Invoke Xdelta

       xdelta subcommand [ option...  ] [ operand...  ]

       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 subcom-
       mand will be detailed seperately.

   Gzip processing
       Attempting to compute a delta between compressed input files usually results in poor  com-
       pression.   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  spe-
       cial case for gzip(1) compressed files.	If any version input to the delta command is rec-
       ognized 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.

       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

       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 exten-
       sion will be added to avoid destroying any existing data.

       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.

       -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.

	      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 dif-
	      ferences in the re-compressed content.

       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


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