aegis -DIFFerence

Section: User Commands (1) Updated: Aegis Local index Up

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.

COPYRIGHT

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.