1Xdelta(1) General Commands Manual Xdelta(1)
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6 xdelta - Invoke Xdelta
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9 xdelta subcommand [ option... ] [ operand... ]
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12 Xdelta provides the ability to generate deltas between a pair of files
13 and later apply those deltas. It operates similar to the diff and
14 patch commands, but works on binary files and does not produce a human
15 readable output.
16 Xdelta has three subcommands, delta, patch, and info. Delta accepts
18 two file versions and produces a delta, while patch accepts the origi‐
19 nal file version and delta and produces the second version. The info
20 command prints useful information about a delta. Each subcommand will
21 be detailed seperately.
22 Gzip processing
25 Attempting to compute a delta between compressed input files usually
26 results in poor compression. This is because small differences between
27 the original contents causes changes in the compression of whole blocks
28 of data. To simplify things, Xdelta implements a special case for
29 gzip(1) compressed files. If any version input to the delta command is
30 recognized as having gzip compression, it will be automatically decom‐
31 pressed into a temporary location prior to comparison. This temporary
32 location is either the value of the TMPDIR environment variable, if
33 set, otherwise "/tmp".
34 The Xdelta patch header contains a flag indicating that the recon‐
36 structed version should be recompressed after applying the patch. In
37 general, this allows Xdelta to operate transparently on gzip compressed
38 inputs.
39 There is one potential problem when automatically processing gzip com‐
41 pressed files, which is that the recompressed content does not always
42 match byte-for-byte with the original compressed content. The uncom‐
43 pressed content still matches, but if there is an external integrity
44 check such as cryptographic signature verification, it may fail. To
45 prevent this from happening, the --pristine option disables automatic
46 gzip processing.
47 MD5 integrity check
50 By default, Xdelta always verifies the MD5 checksum of the files it
51 reconstructs. This prevents you from supplying an incorrect input dur‐
52 ing patch, which would result in corrupt output. Because of this fea‐
53 ture, you can feel confident that patch has produced valid results.
54 The --noverify option disables MD5 verification, but this is only rec‐
55 ommended for performance testing.
56 Compressed patch format
59 Xdelta uses a fairly simple encoding for its delta, then applies zlib
60 compression to the result. You should not have to post-compress an
61 Xdelta delta.
62 Delta
65 The delta subcommand has the following synopsis:
66 xdelta delta [ option... ] fromfile tofile patchout
68 Computes a delta from fromfile to tofile and writes it to patchout
70 Patch
73 The patch subcommand has the following synopsis:
74 xdelta patch [ option... ] patchin [ fromfile [ tofile ]]
76 Applies patchin to fromfile and produces a reconstructed version of
78 tofile.
79 If fromfile was omitted, Xdelta attempts to use the original fromfile
81 name, which is stored in the delta. The from file must be identical to
82 the one used to create the delta. If its length or MD5 checksum dif‐
83 fers, patch will abort with an error message.
84 If tofile was omitted, Xdelta attempts to use the original tofile name,
86 which is also stored in the delta. If the original tofile name already
87 exists, a unique filename extension will be added to avoid destroying
88 any existing data.
89 Info
92 The info subcommand has the following synopsis:
93 xdelta info patchinfo
95 Prints information about patchinfo and the version it reconstructs,
97 including file names, lengths, and MD5 checksums.
98 Options
101 -0..9 Set the zlib compression level. Zero indicates no compression.
102 Nine indicates maximum compression.
103 -h, --help
106 Print a short help message and exit.
107 -q, --quiet
110 Quiet. Surpresses several warning messages.
111 -v, --version
114 Print the Xdelta version number and exit.
115 -V, --verbose
118 Verbose. Prints a bit of extra information.
119 -n, --noverify
122 No verify. Turns off MD5 checksum verification of the input and
123 output files.
124 -m=SIZE, --maxmem=SIZE
127 Set an upper bound on the size of an in-memory page cache. For
128 example, --maxmem=32M will use a 32 megabyte page cache.
129 -s=BLOCK_SIZE
132 Set the block size, unless it was hard coded (20% speed improve‐
133 ment). Should be a power of 2.
134 -p, --pristine
137 Disable the automatic decompression of gzipped inputs, to pre‐
138 vent unexpected differences in the re-compressed content.
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142 The delta command exits with status 0 to indicate that no differences
143 were found, with status 1 to indicate that some differences were found,
144 and with status 2 to indicate an error of some kind. The patch and
145 info commands exit with status 0 on success and 2 on failure.
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149 Author: Joshua P. MacDonald, jmacd@cs.berkeley.edu
150 Manual Page Revision: 1.6; Release Date: Sun, 28 Jan 2007 12:21:11
151 -0800.
152 Copyright © 1997, 1998, 1999, 2000, 2001
153 Xdelta(1)