CVS

Introduction

CVS is part of the GNU Project and is freely distributed in the open source community. (GNU does many commonly used UNIX utilities like emacs, make, gcc, and gdb. See their "Free Software Directory" for a complete list.)

Why use CVS?

• It provides change histories. Suppose you make several changes to a source file and it ends up breaking something? CVS allows you to keep a change history so that you can review how a source file has been modified. This is particularly important in team contexts when other people are changing the same set of files.

• It supports rollbacks. Along with source file change histories, CVS saves previous versions of each source file so that a developer can rollback to any previous version at will. This can be a powerful tool when debugging.

• It provides release tagging. At some point, a snapshot of the current working system can be tagged with a particular version number. This will add a tag to all source files, and allow a developer to rollback the entire project to a particular point for debugging or other purposes.

• It backs up previous versions of source code in a compact format. One could always save a copy of source files at various times to create a change history and allow rollbacks. This is inefficient, however, since multiple copies of things that don't change are also saved and the disk space needed quickly grows. CVS provides a compact solution by internally saving only the differences between file versions, but still allowing any version to be restored in its entirety.

• It provides merging capabilities. Two developers working on the same source file independently can merge their changes. Source code can also be branched, and the branches merged together at some later time.

Some basic commands

First, set your environment variable to your CVS repository directory. This is where CVS will store source files, differences, version information, etc.

setenv CVSROOT=mycvsrootdir

To create a source repository, cd to your source directory and use:

cvs import -m MESSAGE MODULE VENDER_TAG RELEASE_TAG

Once a repository is created, you can cd to any directory and "checkout" the source tree. This will copy it into your directory.

cvs checkout [-r REV] [-d DIR] MODULE

To add source files to a project:

cvs add -m MESSAGE file1 file2 file3

Remember that "checkout" in CVS means copying a source tree into your current working directory. Unlike some other source control systems, there is no concept of checking a file out before working on modifications in CVS. Instead, you simply make the modifications, and then "commit" the changes using:

cvs commit

To create a snapshot, you tag all files in the module:

cvs tag TAG_NAME

To look at a file's history:

cvs history file1

Useful CVS Links