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done

papaya$

The RCS file importrtf.c,v is created, and importrtf.c is removed.

To work on the source file again, use the co command to check it out. For example:

papaya$ co -l importrtf.c

importrtf.c,v --> importrtf.c

revision 1.1 (locked)

done

papaya$

will check out importrtf.c (from importrtf.c,v) and lock it. Locking the file allows you to edit it and to check it back in. If you only need to check the file out in order to read it (for example, to issue a make), you can leave the -l switch off of the co command to check it out unlocked. You can't check in a file unless it is locked first (or if it has never been checked in before, as in the example).

Now you can make some changes to the source and check it back in when done. In many cases, you'll want to keep the file checked out and use ci to merely record your most recent revisions in the RCS file and bump the version number. For this, you can use the -l switch with ci, as so:

papaya$ ci -l importrtf.c

importrtf.c,v <-- importrtf.c

new revision: 1.2; previous revision: 1.1

enter log message, terminated with single '.' or end of file:

>> Changed printf call

>> .

done

papaya$

This automatically checks out the file, locked, after checking it in. This is a useful way to keep track of revisions even if you're the only one working on a project.

If you use RCS often, you may not like all those unsightly importrtf.c,v RCS files cluttering up your directory. If you create the subdirectory RCS within your project directory, ci and co will place the RCS files there, out of the way of the rest of the source.

In addition, RCS keeps track of all previous revisions of your file. For instance, if you make a change to your program that causes it to break in some way and you want to revert to the previous version to "undo" your changes and retrace your steps, you can specify a particular version number to check out with co. For example:

papaya$ co -l1.1 importrtf.c

importrtf.c,v --> importrtf.c

revision 1.1 (locked)

writable importrtf.c exists; remove it? [ny](n): y

done

papaya$

checks out Version 1.1 of the file importrtf.c. You can use the program rlog to print the revision history of a particular file; this displays your revision log entries (entered with ci) along with other information such as the date, the user who checked in the revision, and so forth.

RCS automatically updates embedded "keyword strings " in your source file at checkout time. For example, if you have the string:

/* $Header$

in the source file, co will replace it with an informative line about the revision date, version number, and so forth, as in the following example:

/* $Header: /work/linux/hitch/programming/tools/RCS/rcs.tex 1.2 1994/12/04 15:19:31

mdw Exp mdw $ */

Other keywords exist as well, such as $Author$, $Date$, and .

Many programmers place a static string within each source file to identify the version of the program after it has been compiled. For example, within each source file in your program, you can place the line:

static char rcsid[ ] = "\@(#)$Header$

co replaces the keyword $Header$ with a string of the form given here. This static string survives in the executable, and the what command displays these strings in a given binary. For example, after compiling importrtf.c into the executable importrtf, we can use the following command:

papaya$ what importrtf

importrtf:

$Header: /work/linux/hitch/programming/tools/RCS/rcs.tex

1.2 1994/12/04 15:19:31 mdw Exp mdw $

papaya$

what picks out strings beginning with the characters @(#) in a file and displays them. If you have a program that has been compiled from many source files and libraries, and you don't know how up-to-date each component is, you can use what to display a version string for each source file used to compile the binary.

RCS has several other programs in its suite, including rcs, used for maintaining RCS files. Among other things, rcs can give other users permission to check out sources from an RCS file. See the manual pages for ci(1), co(1), and rcs(1) for more information.