Using Branches

You can use branches when you need to keep track of an alternate version developed in parallel, such as for bug fixes or experimental purposes. Before you can create a branch, however, you must enable the "branch" flag in the history file using the sccs admin command, as follows:

$ sccs admin -f b program.c

The -fb option sets the b (branch) flag in the history file.

Creating a Branch Delta

To create a branch from delta 1.3 for program.c, you would use the sccs edit subcommand shown in the following figure:

$ sccs edit -r 1.3 -b program.c

When you check in your edited version, the branch delta contains SID 1.3.1.1. Subsequent deltas made from this branch are numbered 1.3.1.2, and so on.

Retrieving Versions from Branch Deltas

Branch deltas usually are not included in the version retrieved by get. To retrieve a branch version (the version associated with a branch delta), you must specifically request it with the -r option. If you omit the sequence number, as in the next example, SCCS retrieves the highest delta in the branch:

$ sccs get -r 1.3.1 program.c
1.3.1.1
87

Merging a Branch Back into the Main Trunk

At some point, perhaps when you've finished with the experiment, you might want to introduce the experimental features into production. But in the meantime, work may have progressed on the production version, in which case there may be incompatibilities between the branch version and the latest trunk version.

To help you sort this situation out, the -i option to sccs edit allows you to specify a list of deltas to include when you check out the file. If any of the changes that were included result in conflicts, edit issues a warning message. A conflict can arise if a line must be deleted to satisfy one delta, but inserted to satisfy another. While it is up to you to resolve each conflict, knowing where they are is a big help.