5. Branches

One of the strongest features of Perforce is branching. Branches are very cheap to create, and moving changes between related branches is very easy (as will be explained later). Branches also allow you to do very experimental work in a sandbox-like environment, without having to worry about colliding with others or destabilizing the main tree. They also provide insulation against mistakes while learning the Perforce system. With all of these benefits, it makes sense for each project to have its own branch, and we strongly encourage that with FreeBSD. Frequent submits of changes to the server are also encouraged.

Similar to Subversion, the Perforce repository (the depot) is a single flat tree. Every file, whether a unique creation or a derivative from a branch, is accessible via a simple path under the server //depot directory. When you create a branch, all you are doing is creating a new path under the //depot. This is in sharp contrast to systems like CVS, where each branch lives in the same path as its parent. With Perforce, the server tracks the relationship between the files in the parent and child, but the files themselves live under their own paths.

The first step to creating a branch is to create a branch specification. This is similar to a client specification, but is created via the command p4 branch branchname.

The following important fields are explained:


The name of the branch. It can be any name, but must be unique within the repository. The common convention in FreeBSD is to use username_projectname.


This can hold a simple text description to describe the branch.


This is the branch mapping. Instead of mapping from the depot to the local machine like a client map, it maps between the branch parent and branch child in the depot. For example, you might want to create a branch of the smpng project. The mapping might look like:

//depot/projects/smpng/... //depot/projects/my-super-smpng/...

Or, you might want to create a brand new branch off of the stock FreeBSD sources:

//depot/vendor/freebsd/... //depot/projects/my-new-project/...

This will map the FreeBSD HEAD tree to your new branch.

Creating the branch spec only saves the spec itself in the server, it does not modify the depot or change any files. The directory that you specified in the branch is empty on the server until you populate it.

To populate your branch, first edit your client with p4 client and make sure that the branch directory is mapped in your client. You might need to add a View line like:

//depot/projects/my-new-project/... //myclient/my-new-project/...

The next step is to run p4 integrate, as described in the next section.

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