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xdelta (1)
  • >> xdelta (1) ( Linux man: Команды и прикладные программы пользовательского уровня )
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    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 original 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 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.

     

    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 prevent unexpected differences in the re-compressed content.

     

    IDENTIFICATION

    Author: Joshua P. MacDonald, [email protected]
    Manual Page Revision: 1.5; Release Date: Fri, 29 Jun 2001 06:01:08 -0700.
    Copyright © 1997, 1998, 1999, 2000, 2001


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    Gzip processing
    MD5 integrity check
    Compressed patch format
    Delta
    Patch
    Info
    Options
    IDENTIFICATION


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