The basic user interface is extremely simple. The novice only needs to learn two commands: ci(1) and co(1). ci, short for ``check in'', deposits the contents of a file into an archival file called an RCS file. An RCS file contains all revisions of a particular file. co, short for ``check out'', retrieves revisions from an RCS file.
Then invoke the check-in command
This command creates an RCS file in the RCS directory, stores f.c into it as revision 1.1, and deletes f.c. It also asks you for a description. The description should be a synopsis of the contents of the file. All later check-in commands will ask you for a log entry, which should summarize the changes that you made.
Files in the RCS directory are called RCS files; the others are called working files. To get back the working file f.c in the previous example, use the check-out command
This command extracts the latest revision from the RCS file and writes it into f.c. If you want to edit f.c, you must lock it as you check it out with the command
You can now edit f.c.
Suppose after some editing you want to know what changes that you have made. The command
tells you the difference between the most recently checked-in version and the working file. You can check the file back in by invoking
This increments the revision number properly.
If ci complains with the message
then you have tried to check in a file even though you did not lock it when you checked it out. Of course, it is too late now to do the check-out with locking, because another check-out would overwrite your modifications. Instead, invoke
This command will lock the latest revision for you, unless somebody else got ahead of you already. In this case, you'll have to negotiate with that person.
Locking assures that you, and only you, can check in the next update, and avoids nasty problems if several people work on the same file. Even if a revision is locked, it can still be checked out for reading, compiling, etc. All that locking prevents is a check-in by anybody but the locker.
If your RCS file is private, i.e., if you are the only person who is going to deposit revisions into it, strict locking is not needed and you can turn it off. If strict locking is turned off, the owner of the RCS file need not have a lock for check-in; all others still do. Turning strict locking off and on is done with the commands
If you don't want to clutter your working directory with RCS files, create a subdirectory called RCS in your working directory, and move all your RCS files there. RCS commands will look first into that directory to find needed files. All the commands discussed above will still work, without any modification. (Actually, pairs of RCS and working files can be specified in three ways: (a) both are given, (b) only the working file is given, (c) only the RCS file is given. Both RCS and working files may have arbitrary path prefixes; RCS commands pair them up intelligently.)
To avoid the deletion of the working file during check-in (in case you want to continue editing or compiling), invoke
These commands check in f.c as usual, but perform an implicit check-out. The first form also locks the checked in revision, the second one doesn't. Thus, these options save you one check-out operation. The first form is useful if you want to continue editing, the second one if you just want to read the file. Both update the identification markers in your working file (see below).
You can give ci the number you want assigned to a checked in revision. Assume all your revisions were numbered 1.1, 1.2, 1.3, etc., and you would like to start release 2. The command
assigns the number 2.1 to the new revision. From then on, ci will number the subsequent revisions with 2.2, 2.3, etc. The corresponding co commands
retrieve the latest revision numbered 2.x and the revision 2.1, respectively. co without a revision number selects the latest revision on the trunk, i.e. the highest revision with a number consisting of two fields. Numbers with more than two fields are needed for branches. For example, to start a branch at revision 1.3, invoke
This command starts a branch numbered 1 at revision 1.3, and assigns the number 18.104.22.168 to the new revision. For more information about branches, see rcsfile(5).
into your text, for instance inside a comment. RCS will replace this marker with a string of the form
With such a marker on the first page of each module, you can always see with which revision you are working. RCS keeps the markers up to date automatically. To propagate the markers into your object code, simply put them into literal character strings. In C, this is done as follows:
The command ident extracts such markers from any file, even object code and dumps. Thus, ident lets you find out which revisions of which modules were used in a given program.
You may also find it useful to put the marker $Log$ into your text, inside a comment. This marker accumulates the log messages that are requested during check-in. Thus, you can maintain the complete history of your file directly inside it. There are several additional identification markers; see co(1) for details.