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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 com- mands, but works on binary files and does not produce a human readable out- put. 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 seper- ately. Gzip processing Attempting to compute a delta between compressed input files usually re- sults 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 com- pressed files, which is that the recompressed content does not always match byte-for-byte with the original compressed content. The uncompressed con- tent 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 recon- structs. 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 op- tion disables MD5 verification, but this is only recommended for perfor- mance testing. Compressed patch format Xdelta uses a fairly simple encoding for its delta, then applies zlib com- pression 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 ex- ists, a unique filename extension will be added to avoid destroying any ex- isting data. Info The info subcommand has the following synopsis: xdelta info patchinfo Prints information about patchinfo and the version it reconstructs, includ- ing 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 ex- ample, --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 prevent 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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