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/