xdelta



Xdelta(1)                                                            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  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 origi-
       nal 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 decom-
       pressed 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  recon-
       structed  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 uncom-
       pressed 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 dur-
       ing  patch, which would result in corrupt output.  Because of this fea-
       ture, you can feel confident that patch  has  produced  valid  results.
       The  --noverify option disables MD5 verification, but this is only rec-
       ommended 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 dif-
       fers, 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 improve-
              ment).  Should be a power of 2.


       -p, --pristine
              Disable the automatic decompression of gzipped inputs,  to  pre-
              vent 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)

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