rcs

Initialize RCS for a file (check in initial version)

$ ci [filename]

$ co -l [filename]

$ co [filename]

$ ci -m "[message]" [filename]

$ rlog [filename]

$ rcsdiff [filename]

$ co -r[1.2] [filename]

rcs [options] file...
ci [options] file...
co [options] file...

RCS (Revision Control System) manages multiple revisions of files, providing version control for individual files. It automates storing, retrieving, logging, and merging revisions, making it useful for source code, documentation, and configuration files.
The workflow centers on ci (check-in) and co (check-out). Check-in stores a new revision and removes the working file by default. Check-out retrieves a revision; use -l to lock the file for exclusive editing.
RCS stores revisions efficiently using reverse deltas—the latest revision is stored complete, while older revisions are stored as differences. This makes retrieving the current version fast.
Revisions are numbered hierarchically (1.1, 1.2, 1.3, etc.). The first number is the release, the second is the level. Branches create additional number fields (1.2.1.1).

ci (check-in)

Store a new revision in the RCS file

Retrieve a revision from the RCS file

Change RCS file attributes

Compare RCS revisions

Merge RCS revisions

Print revision log messages

Lock the revision for exclusive editing (with co)

Unlock after check-in (with ci)

Specify revision number

Specify log message

Quiet mode, suppress diagnostics

RCS operates on individual files, not directories or projects. For multi-file version control, modern tools like Git are more appropriate.
The default check-in behavior removes the working file. Use ci -u to keep an unlocked copy or ci -l to keep a locked copy for continued editing.
RCS files (ending in ,v) are stored in the same directory or in an RCS/ subdirectory. Ensure proper permissions for collaborative use.

RCS was developed by Walter F. Tichy at Purdue University, first released in 1982. It was one of the earliest version control systems and influenced later tools like CVS (which added network support) and eventually Git. RCS is part of the GNU project and continues to be available on most Unix-like systems.

cvs(1), git(1), svn(1), diff(1)