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PROGRAM:

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.

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