Provided by: xdelta_1.1.3-9.1ubuntu1_amd64 
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.
-mSIZE, --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, 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)