Provided by: aegis_4.24.3-3_amd64 
NAME
aegis difference - find differences between a change and the baseline
SYNOPSIS
aegis -DIFFerence [ filename... ] [ option... ]
aegis -DIFFerence -List [ option... ]
aegis -DIFFerence -Help
DESCRIPTION
The aegis -DIFFerence command is used to generate difference listings between source files in the the
development directory and the baseline. The purpose is to enable reviewers to find each and every edit
performed on the source files. The difference listings will be placed into files named for the sources
files but with an additional ",D" suffix.
The command used to perform the differences is specified in the diff_command field of the project
configuration file (see aepconf(5) for more information).
It is possible to configure a project to omit the diff step as unnecessary, by the following setting:
diff_command = "exit 0";
This disables all generation, checking and validation of difference file for each change source file.
The merge functions of the aediff(1) command are unaffected by this setting.
Please note that the history_content_limitation field of the project configuration file does not apply
to the diff_command field.
If no files are named on the command line, all files in the change will be differenced.
You may name a directory on the command line, and all files in the change in that directory tree will be
differenced.
File Name Interpretation
The aegis program will attempt to determine the project file names from the file names given on the
command line. All file names are stored within aegis projects as relative to the root of the baseline
directory tree. The development directory and the integration directory are shadows of this baseline
directory, and so these relative names apply here, too. Files named on the command line are first
converted to absolute paths if necessary. They are then compared with the baseline path, the
development directory path, and the integration directory path, to determine a baseline-relative name.
It is an error if the file named is outside one of these directory trees.
The -BAse_RElative option may be used to cause relative filenames to be interpreted as relative to the
baseline path; absolute filenames will still be compared with the various paths in order to determine a
baseline-relative name.
The relative_filename_preference in the user configuration file may be used to modify this default
behavior. See aeuconf(5) for more information.
Notification
The actions of the command are controlled by the diff_command and merge_command fields of the project
config file. See aepconf(5) for more information.
THE BASELINE LOCK
The baseline lock is used to ensure that the baseline remains in a consistent state for the duration of
commands which need to read the contents of files in the baseline.
The commands which require the baseline to be consistent (these include the aeb(1), aecp(1) and aed(1)
commands) take a baseline read lock. This is a non-exclusive lock, so the concurrent development of
changes is not hindered.
The command which modifies the baseline, aeipass(1), takes a baseline write lock. This is an exclusive
lock, forcing aeipass(1) to block until there are no active baseline read locks.
It is possible that one of the above development commands will block until an in-progress aegis
-Integrate_PASS completes. This is usually of short duration while the project history is updated. The
delay is essential so that these commands receive a consistent view of the baseline. No other
integration command will cause the above development commands to block.
When aegis' branch functionality is in use, a read (non-exclusive) lock is taken on the branch baseline
and also each of the "parent" baselines. However, a baseline write (exclusive) lock is only taken on
the branch baseline; the "parent" baselines are only read (non-exclusive) locked.
File Action Adjustment
When this command runs, it first checks the change files against the projects files. If there are
inconsistencies, the file actions will be adjusted as follows:
create If a file is being created, but another change set is integrated which also creates the file,
the file action in the change set still being developed will be adjusted to "modify".
modify If a file is being modified, but another change set is integrated which removes the file, the
file action in the change set still being developed will be adjusted to "create".
remove If a file is being removed, but another change set is integrated which removes the file, the
file will be dropped from the change set still being developed.
CONFLICT RESOLUTION
If the version of a file in the change is not the same as the version of the file in the baseline, it is
out-of-date; some other change has altered the file while this change was being developed.
When a difference is requested for an out-of-date file, a merge is performed between the common
ancestor, the version in the baseline, and the version in the development directory. The command used
to perform the merge is specified by the merge_command field of the project configuration file (see
aepconf(5) for more information).
Please note that the history_content_limitation field of the project configuration file does not apply
to the merge_command field.
After the merge is performed the version of the file will be changed to be the current version, marking
the file as up to date, and a new build will be required.
The original file in your development directory is preserved with an ",B" suffix (B for backup). The
source file contains the result of the merge. You should edit the source files, to make sure the
automatic merge has produced sensible results.
This merge process works most of the time. Usually two changes to two logically separate areas of
functionality will alter two logically separate parts of any files they may have in common. There are
pathological cases where this merge process is spectacularly useless, but these are surprisingly rare in
practice.
If you don't want the automatic merge results, simply use the mv(1) command to restore the contents from
the ",B" file.
If any merges are required no differences will be performed. An error message and a non-zero exit
status will also result. This is to ensure that developers notice that merges have been done, and that
they reconcile the sources and the merged ,D files before the next difference. See the -No_Merge and
-Only_Merge options, below, for exact control of when merging is performed.
Cloning and Merging
When you use aeclone(1) to clone a change set, and then integrate one of the two change sets, you will observe that Aegis says that the files of the un-integrated change are now out-of-date. If you run aem(1) to bring the out-of-date files back up-to-date, fmerge(1) and some (but not) all other merging tools, it signals just about everything as a conflict, even though both alternatives are identical. The problem is that two changes making identical edits to the same place in the same file are a logical conflict, even if not an actual conflict, and it takes a human to figure out the difference. Think of a shopping list: the ensuite needs more soap, and so does the main bathroom. The second "soap" on the merge of the two shopping lists isn't a duplicate, you really do need two boxes of soap. Sometimes edits of source files are the same: sometimes the logical conflict is resolved by applying both identical edits, not just one. This is just the fmerge(1) command being more conservative than RCS's merge(1) command. The easiest way to deal with this common situation it to run an aecpu -unchanged command before you run the aem(1) merge command, and you will have less grief. It's also worth remembering that Aegis stashes the original file with a ,B suffix (B for backup) so you can simply mv fubar,B fubar if you know that all of the conflicts are logical conflicts.
INTEGRATION
During integration, it is also necessary to difference a change. This provides the difference between
the branch and its parent, for when development on a branch is completed and it is to be reviewed. The
baseline of a branch is the development directory of the composite change it represents.
OPTIONS
The following options are understood:
-ANticipate change-number
This option is used to nominate a source for the reference files, rather than the baseline.
This may be used to synchronize with a change without having to wait for it to arrive in the
baseline. It is an error if the anticipated change is not in one of the 'being reviewed' or
'awaiting integration' or 'being integrated' states. A merge is always performed, because the
anticipated change is "about" to make any common file out-of-date. You will still have to
perform a "real" merge later.
-BRanch number
This option may be used to specify a different branch for the origin file, rather than the
baseline. (See also -TRunk option. Please Note: the -BRanch option does not take a project
name, just the branch number suffix.
-GrandParent
This option may be used to specify the grandparent branch (one up from the current branch) for
the origin file, rather than the baseline. (The -grandparent option is the same as the “-branch
..” option.)
-Change number
This option may be used to specify a particular change within a project. See aegis(1) for a
complete description of this option.
-Help
This option may be used to obtain more information about how to use the aegis program.
-List
This option may be used to obtain a list of suitable subjects for this command. The list may be
more general than expected.
-Not_Logging
This option may be used to disable the automatic logging of output and errors to a file. This
is often useful when several aegis commands are combined in a shell script.
-TRunk
This option may be used to specify the project trunk for the origin file, rather than the
baseline. (See also -BRanch option, the -trunk option is the same as the “-branch -” option.)
-No_Merge
This option is used to cause only file differences to be generated, even when file versions are
out-of-date. If not set, the default is to use the diff_preference field of the aeuconf(5)
file.
-Only_Merge
This option is used to cause only file merges to be performed on files with out-of-date
versions. Other source files are ignored. If not set, the default is to use the
diff_preference field of the aeuconf(5) file.
-Automatic_Merge
This option is used to perform -Only_Merge if any source files have out-of-date versions,
otherwise -No_Merge is performed. Only merges or differences will be performed, it will never
use a mixture. If not set, the default is to use the diff_preference field of the aeuconf(5)
file.
-Project name
This option may be used to select the project of interest. When no -Project option is
specified, the AEGIS_PROJECT environment variable is consulted. If that does not exist, the
user's $HOME/.aegisrc file is examined for a default project field (see aeuconf(5) for more
information). If that does not exist, when the user is only working on changes within a single
project, the project name defaults to that project. Otherwise, it is an error.
-TERse
This option may be used to cause listings to produce the bare minimum of information. It is
usually useful for shell scripts.
-Verbose
This option may be used to cause aegis to produce more output. By default aegis only produces
output on errors. When used with the -List option this option causes column headings to be
added.
-Wait This option may be used to require Aegis commands to wait for access locks, if they cannot be
obtained immediately. Defaults to the user's lock_wait_preference if not specified, see
aeuconf(5) for more information.
-No_Wait
This option may be used to require Aegis commands to emit a fatal error if access locks cannot
be obtained immediately. Defaults to the user's lock_wait_preference if not specified, see
aeuconf(5) for more information.
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 aegis are long, this means
ignoring the extra leading '-'. The "--option=value" convention is also understood.
RECOMMENDED ALIAS
The recommended alias for this command is
csh% alias aed 'aegis -diff \!* -v'
sh$ aed(){aegis -diff "$@" -v}
For user's convenience, particularly when they have selected the “no merge” preference, there is also a
merge alias:
csh% alias aem 'aegis -diff -only_merge \!* -v'
sh$ aem(){aegis -diff -only_merge $* -v}
ERRORS
It is an error if the change is not in the being developed or being integrated states.
EXIT STATUS
The aegis command will exit with a status of 1 on any error. The aegis 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.
SEE ALSO
aeb(1) build also takes a baseline read lock (non-exclusive) aecp(1) copy file also takes a baseline read lock (non-exclusive) aedb(1) begin development of a change aeipass(1) integrate pass takes a baseline write lock (exclusive) aepconf(5) project configuration file format aeuconf(5) user configuration file format
COPYRIGHT
aegis 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 aegis program comes with ABSOLUTELY NO WARRANTY; for details use the 'aegis -VERSion License'
command. This is free software and you are welcome to redistribute it under certain conditions; for
details use the 'aegis -VERSion License' command.
AUTHOR
Peter Miller E-Mail: millerp@canb.auug.org.au /\/\* WWW: http://www.canb.auug.org.au/~millerp/