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aesvt(1)							      aesvt(1)

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 al-
	ter 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	num-
		ber).  On check-out, if	no version number is specified,	the
		most recent version is given.  On check-in, if no version num-
		ber 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 com-
			mands).

		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 op-
		tion.

	-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 op-
	tional.	 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	inter-
	preted 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	"--op-
	tion=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	er-
	rors.

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 bi-
	nary, 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, be-
	cause 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 or-
	der, from most recent (greatest	edit number) to	least recent (version
	number one).  To determine where one version stops and the next	ver-
	sion 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 por-
	tions; 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	be-
	cause you are curious.

	You can	actually choose	from a number of compression algorithms, in-
	cluding	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 com-
	pression used by earlier versions.

   End-To-End Issues
	See also Saltzer, J.H. et al (1981) End-to-end arguments in system de-
	sign, 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 4.25.D510
	Copyright (C) 1991, 1992, 1993,	1994, 1995, 1996, 1997,	1998, 1999,
	2000, 2001, 2002, 2003,	2004, 2005, 2006, 2007,	2008, 2009, 2010,
	2011, 2012 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:	 pmiller@opensource.org.au
	/\/\*		  WWW:	 http://miller.emu.id.au/pmiller/

Reference Manual		     Aegis			      aesvt(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | ENVIRONMENT VARIABLES | FILE FORMAT | COPYRIGHT | AUTHOR

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