RCS was first released in 1982 by Walter Tichy at Purdue University making it one of the earliest version control systems (VCS) used for software development. Unlike modern VCS which are designed for distributed, concurrent development, RCS uses a centralized code repository where files are singularly checked in/out. Although largely supplanted RCS is still useful for small personal projects and is still natively included in the NetBSD operating system which SDF largely runs on. RCS is still actively maintained as a GNU Project at https://www.gnu.org/software/rcs/ .

Although largely supplanted by distributed systems like Git and Mercurial, RCS is still surprisingly useful for small personal projects as well as local scripts and configuration files. In many ways RCS is easier to use with only a handful of commands to memorize, each with a short list of options that lend themselves to aliasing or script incorporation.

There are several commands that come with RCS but the following are likely most useful:

• ci(1) - RCS file check-in
• co(1) - RCS file check-out
• rlog(1) - RCS change log
• rcsdiff(1) - RCS diff(1) generator

The rcs(1) command is also useful, sort of a multi-tool that duplicates some of the functionality of the above commands as well as extending them, i.e. deleting a range of revisions, editing informational text in the log, changing default locking modes, etc.

Not much preparation is needed to get started managing file revisions with RCS. While not mandatory it is highly recommended that a RCS sub-directory be created in each working directory where, if present, RCS will store the “”deltas“” – special files of the form fubar,v – that store the differences (deltas) between revisions of a file under RCS management. If the RCS sub-directory is not present RCS simply stores those delta files in the working directory.

The rcsintro(1) manpage covers much of the basics of RCS; below is a quick tour:

• create a working directory & RCS sub-dir: $ mkdir -p ~/rcs_fun/RCS
• change to working dir & create a file: $ cd ~/rcs_fun ; echo 'RCS is awesome!' > fubar
• make initial commit of test file: $ ci -u fubar
• check file back out & edit again: $ co -l fubar && echo 'this file is fubar' » fubar
• view diffs (working file vs last checked ver.): $ rcsdiff fubar
• commit new revision of file: $ ci -u fubar
• view log of changes: $ rlog fubar

Specific revisions can be acted upon by passing them to the various commands in the form -r<start>[ -r<end>] ; by default RCS compares the working copy to the last checked in version.

While comprehensive coverage of all RCS can do is beyond the scope of this introductory tutorial, the basics can be grasped fairly easily and are perhaps best conveyed via an annotated RCS Sample Session.

• no space allowed between options and arguments, i.e. use $ co -r1.3 not $ co -r 1.3
• delta files (fubar,v) end up in the working directory if no ../RCS directory is present
• lock files when you check them out, unlock them when you check them in
• don't use -r by itself with the ci(1) command – it's a reset option

Aside from the man(1) and info(1) pages, Tichy's original 1985 paper¹⁾ still provides an good introduction to using RCS. For more in-depth coverage the following may prove helpful:

• GNU RCS Manual : https://www.gnu.org/software/rcs/manual/rcs.html
• RCS Handbook by Brian O’Donovan © 1992, (unpublished) : https://www.compuphase.com/software/RCS_Handbook.pdf
• Applying RCS and SCCS by Bolinger & Bronsoni, © 1995 O'Reilly Media : https://www.biblio.com/9781565921177

How about a graphical RCS browser²⁾ for Windows and Linux?