3 Xdelta -- A binary delta generator
5 Announcing version 1.1.2 of Xdelta. Xdelta is an application program
6 designed to compute changes between files. These changes (deltas) are
7 similar to the output of the "diff" program in that they may be used
8 to store and transmit only the changes between files. However, unlike
9 diff, the output of Xdelta is not expressed in a human-readable
10 format--Xdelta can also also apply these deltas to a copy of the
11 original file. Xdelta uses a fast, linear algorithm and performs well
12 on both binary and text files.
14 Xdelta 1.1.2 is a stable, maintenence release. New, ongoing work on
15 Xdelta has focused on a new storage system with features similar to
16 the RCS command set. For more information on new development, see the
17 Xdelta-2.0 release series at http://xdelta.sourceforge.net.
19 Xdelta was designed and implemented by Joshua MacDonald. The delta
20 algorithm is based on the Rsync algorithm, though implementation and
21 interface considerations leave the two programs quite distinct. The
22 Rsync algorithm is due to Andrew Tridgell and Paul Mackerras.
24 To compile and install Xdelta, read the instructions in the INSTALL
25 file. Once you have done this, you should at least read the first few
26 sections of the documentation. It is available in info format. All
27 documentation is located in the doc/ subdirectory.
29 This release, version 1.1.2, and future releases of Xdelta can be
30 found at http://xdelta.sourceforge.net.
32 Xdelta is released under the GNU Library Public License (GPL), see the
33 file COPYING for details.
35 There is mailing list for announcements:
37 xdelta-announce@lists.sourceforge.net
39 you can subscribe to the mailing list or file bug reports through
42 http://sourceforge.net/projects/xdelta/
44 Comments about Xdelta can be addressed to the following addresses:
48 The man page describes how to use Xdelta in more detail:
51 xdelta - Invoke Xdelta
54 xdelta subcommand [ option... ] [ operand... ]
58 Xdelta provides the ability to generate deltas between a pair
59 of files and later apply those deltas. It operates similar to
60 the diff and patch commands, but works on binary files and does
61 not produce a human readable output.
63 Xdelta has three subcommands, delta, patch, and info. Delta
64 accepts two file versions and produces a delta, while patch
65 accepts the original file version and delta and produces the
66 second version. The info command prints useful information
67 about a delta. Each subcommand will be detailed seperately.
71 Attempting to compute a delta between compressed input files
72 usually results in poor compression. This is because small
73 differences between the original contents causes changes in the
74 compression of whole blocks of data. To simplify things,
75 Xdelta implements a special case for gzip(1) compressed files.
76 If any version input to the delta command is recognized as
77 having gzip compression, it will be automatically decompressed
78 into a temporary location prior to comparison. This temporary
79 location is either the value of the TMPDIR environment
80 variable, if set, otherwise "/tmp".
82 The Xdelta patch header contains a flag indicating that the
83 reconstructed version should be recompressed after applying
84 the patch. In general, this allows Xdelta to operate
85 transparently on gzip compressed inputs.
87 There is one potential problem when automatically processing
88 gzip compressed files, which is that the recompressed content
89 does not always match byte-for-byte with the original
90 compressed content. The uncompressed content still matches,
91 but if there is an external integrity check such as
92 cryptographic signature verification, it may fail. To prevent
93 this from happening, the --pristine option disables automatic
98 By default, Xdelta always verifies the MD5 checksum of the
99 files it reconstructs. This prevents you from supplying an
100 incorrect input during patch, which would result in corrupt
101 output. Because of this feature, you can feel confident that
102 patch has produced valid results. The --noverify option
103 disables MD5 verification, but this is only recommended for
106 Compressed patch format
108 Xdelta uses a fairly simple encoding for its delta, then
109 applies zlib compression to the result. You should not have to
110 post-compress an Xdelta delta.
114 The delta subcommand has the following synopsis:
116 xdelta delta [ option... ] fromfile tofile patchout
118 Computes a delta from fromfile to tofile and writes it to patchout
122 The patch subcommand has the following synopsis:
124 xdelta patch [ option... ] patchin [ fromfile [ tofile ]]
126 Applies patchin to fromfile and produces a reconstructed
129 If fromfile was omitted, Xdelta attempts to use the original
130 fromfile name, which is stored in the delta. The from file
131 must be identical to the one used to create the delta. If its
132 length or MD5 checksum differs, patch will abort with an error
135 If tofile was omitted, Xdelta attempts to use the original
136 tofile name, which is also stored in the delta. If the
137 original tofile name already exists, a unique filename
138 extension will be added to avoid destroying any existing data.
141 The info subcommand has the following synopsis:
143 xdelta info patchinfo
145 Prints information about patchinfo and the version it
146 reconstructs, including file names, lengths, and MD5 checksums.
149 -0..9 Set the zlib compression level. Zero indicates no
150 compression. Nine indicates maximum compression.
153 Print a short help message and exit.
156 Quiet. Surpresses several warning messages.
159 Print the Xdelta version number and exit.
162 Verbose. Prints a bit of extra information.
165 No verify. Turns off MD5 checksum verification of the
166 input and output files.
168 -m=SIZE, --maxmem=SIZE
169 Set an upper bound on the size of an in-memory page
170 cache. For example, --maxmem=32M will use a 32 megabyte
174 Set the block size, unless it was hard coded (20% speed
175 improvement). Should be a power of 2.
178 Disable the automatic decompression of gzipped
179 inputs, to prevent unexpected differences in the
180 re-compressed content.