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       aesvt - simple version tool


       aesvt -CHeck_Out -HIstory file -File output-file [ -e edit ]
       aesvt -CHeck_In -HIstory file -File input-file [ -e edit ] [ name=value
       aesvt -List -HIstory file
       aesvt -Query -HIstory file
       aesvt -Version


       The aesvt program may be used to manage history version files.  This is
       a minimalist history tool, which makes no provision for managing a work

       It is able to cope with binary files, and with reasonable efficiently
       if they are not too large.

       It has good end-to-end properties because it keeps a checksum for each
       file version, and a checksum for the whole history file.

       There is no provision for keyword substitution of any kind.  A check-
       out will exactly reproduce the input file.  A check-in will never alter
       the input file.


       The following options are understood:

       -History history-file
              This option is used to specify the name of the history file.

       -File file-name
               This option is used to specify the name of the input or output
               file.  On check-out, the file name "-" is understood to mean
               the standard output.  There is no equivalent for check-in.

       -Edit edit-number
               This option is used to specify the edit number (version
               number).  On check-out, if no version number is specified, the
               most recent version is given.  On check-in, if no version
               number is specifiued (and it usually isn’t), the previous
               version will have one added to it, or version 1 will be used if
               this is the first check-in.

               This option is used to check a file into the history.

               This option is used to check-out a file from the history.

       -compression-algorithm name
               This option may be used to specify the compression to be used.
               They are listed on order of compression effeciency.

               none    Use no compression (not always meaningful for all

               gzip    Use the compression used by the gzip(1) program.

               bzip2   Use the compression used by the bzip2(1) program.

               More compression algorithms may be added in the future.

               This option is deprecated in favour of the -comp-alg=gzip or
               -comp-alg=bzip2 options.

               This options is deprecated in favour of the -comp-alg=none

       -List   This option is used to list the file’s history.

       -Query  This option is used to query edit number of most recent check-

               This option is used to print version number.

       All other options will produce a diagnostic error.

       See also aegis(1) for options common to all aegis commands.

       All options may be abbreviated; the abbreviation is documented as the
       upper case letters, all lower case letters and underscores (_) are
       optional.  You must use consecutive sequences of optional letters.

       All options are case insensitive, you may type them in upper case or
       lower case or a combination of both, case is not important.

       For example: the arguments "-project, "-PROJ" and "-p" are all
       interpreted to mean the -Project option.  The argument "-prj" will not
       be understood, because consecutive optional characters were not

       Options and other command line arguments may be mixed arbitrarily on
       the command line, after the function selectors.

       The GNU long option names are understood.  Since all option names for
       aesvt are long, this means ignoring the extra leading ’-’.  The
       "--option=value" convention is also understood.


       The aesvt command will exit with a status of 1 on any error.  The aesvt
       command will only exit with a status of 0 if there are no errors.


       See aegis(1) for a list of environment variables which may affect this
       command.  See aepconf(5) for the project configuration file’s project_
       specific field for how to set environment variables for all commands
       executed by Aegis.


       Each version in the history file consists of an RFC822 header, plus the
       file contents.  The header includes (at least) the Content-Length, used
       to remember the length of the file data in bytes; the Checksum, used to
       remember the Adler32 checksum of the file data; and Version, used to
       remember the version number.  The file data can be text or binary,
       because its length is determined by the header.  There is no quoting
       mechanism of any kind for the data.  Except for the mandatory fields,
       additional user-defined us-ascii meta-data may also be stored in the
       header.  There is no diff or delta of any kind for any version.

       This combination of header and data has good end-to-end behaviour,
       because there is a checksum to validate the file data against.  Bad
       blocks in the data will be detected then next time a check-in or check-
       out is attempted.

       The format of the history file consists of one or more file versions
       with the above layout, joined head-to-tail with no separators or
       boundary indicators of any kind.  The versions are in descending order,
       from most recent (greatest edit number) to least recent (version number
       one).  To determine where one version stops and the next version
       starts, use the Content-Length field in the header.  The entire history
       file is then compressed using the bunzip2 algorithm (via libbz2).
       There is no diff or delta of any kind in the history file.

       The advantage of compressing the file is that there is usually a very
       high redundancy between file versions.  For example, if two identical
       versions are checked in (not necessarily sequentially) the second copy
       will compress to only a few bytes.  Unlike diff(1) style deltas, this
       also copes very will with moving blocks of data within the file.  The
       use of bunzip2 formatting means there is also a checksum for the whole
       history file, which allows you to detect bad blocks in the header
       portions; it also means there is a simple way to extract the data from
       a history file even without the aesvt program, or for testing, or
       because you are curious.

       You can actually choose from a number of compression algorithms,
       including GNU Zip and bunzip2, via the -compression-algorithm option.
       More copmpresison algoritthms may be added in the future.  The best
       available comression is used, because this results in the most compact
       history files.  Future versions will always be able to access the
       compression used by earlier versions.

   End-To-End Issues
       See also Saltzer, J.H. et al (1981) End-to-end arguments in system

       This style of history file was inspired by RFC 3284 - The VCDIFF
       Generic Differencing and Compression Data Format.  While the aesvt
       format does not use RFC3284 internally, the arguments for compression
       across file versions are just as relevant.


       aesvt version 4.24.3.D001
       Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
       2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Peter

       The aesvt program comes with ABSOLUTELY NO WARRANTY; for details use
       the ’aesvt -VERSion License’ command.  This is free software and you
       are welcome to redistribute it under certain conditions; for details
       use the ’aesvt -VERSion License’ command.


       Peter Miller   E-Mail:
       /\/\*             WWW: