The principle benefit of RCS for most users is that it provides an easy
way to view or obtain any previous version of a file that is revised over
time. If an RCS maintained file is accidentally deleted or badly modified,
then backup copies of any previous version are readily available.
Suppose "grades" is a file used to store grades for a course and that it is updated weekly. It is important that a recent backup copy of this file always be present in case it ever becomes corrupted. The best way to ensure a backup is always present is to type the following command each time before editing the file.
> ci -l grades
The "ci" (check-in) command stores a backup of "grades" in a file called "grades,v", though that file should never be accessed except by using RCS commands. "grades,v" is created the first time ci is run on a file, and is appended to on later check-ins. When ci is first run on a file, ci will ask for a description of the file. A description can be entered, if desired, and is completed by typing a line consisting of only a period (as the ci command instructs). Furthermore, on each successive occasion that a file is checked in, ci will ask for a summary of the changes, which is entered just like the original description.
If "grades" is ever corrupted or deleted, the command "co -l grades" (check-out) can be used to retrieve the most recently checked in version.
The original file is assigned a version number 1.1, and successive checked-in versions are numbered 1.2, 1.3, 1.4, etc. To view a log of all the changes and change descriptions for the file "grades", type
> rlog grades
To view revision 1.2 of the "grades" file, type
> co -p -r1.2 grades OR > co -p -r1.2 grades | less
To restore revision 1.4 of the "grades" file, type
> co -l -r1.4 grades
To see the changes between the working copy of "grades" and the last checked-in version, type
> rcsdiff grades
To see the changes between the working copy of "grades" and revision 1.4 of "grades", type
> rcsdiff -r1.4 grades
To avoid clutter, and since the RCS files with the ",v" extension are never directly accessed anyways, it is convenient to create a directory names "RCS" for the ",v" files. If such a directory exists in the current directory, then RCS will automatically create and maintain the ",v" files inside it.
