NAME
aesvt - simple version tool
SYNOPSIS
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
DESCRIPTION
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
area.
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.
OPTIONS
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.
-CHeck_In
This option is used to check a file into the history.
-CHeck_Out
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
commands).
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.
-COMPress
This option is deprecated in favour of the -comp-alg=gzip or
-comp-alg=bzip2 options.
-No_COMPress
This options is deprecated in favour of the -comp-alg=none
option.
-List This option is used to list the file’s history.
-Query This option is used to query edit number of most recent check-
in.
-Version
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
supplied.
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.
EXIT STATUS
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.
ENVIRONMENT VARIABLES
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.
FILE FORMAT
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
design, http://web.mit.edu/Saltzer/www/publications/endtoend/‐
endtoend.pdf
Xdelta
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.
COPYRIGHT
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
Miller
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.
AUTHOR
Peter Miller E-Mail: millerp@canb.auug.org.au
/\/\* WWW: http://www.canb.auug.org.au/~millerp/