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
    reconstructs. This prevents you from supplying an incorrect input dur-
    ing patch, which would result in corrupt output. Because of this fea-
    ture, 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 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,
    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 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.

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