Editing Revision Control System (section)

===Legal and licensing===
Initially (through version 3, which was distributed in 4.3BSD), its license prohibited redistribution without written permission from Walter Tichy:<ref>{{cite web |url=http://www.retro11.de/ouxr/43bsd/usr/src/new/rcs/src/rcsdiff.c.html |title=4.3BSD - /usr/src/new/rcs/src/rcsdiff.c |publisher=Walter's Retro Computing Corner Documentation |access-date = 15 November 2014 |date=19 May 1986}}</ref>

{{quote|Copyright (C) 1982 by Walter F. Tichy [...] All rights reserved. No part of this software may be sold or distributed in any form or by any means without the prior written permission of the author.}}

A [[README|READ_ME]] file accompanied some versions of RCS which further restricted distribution, e.g., in [[Berkeley Software Distribution#4.3BSD|4.3BSD-Reno]].<ref>{{Cite FTP |url=ftp://ftp.mrynet.com/operatingsystems/CSRG/cd2/4.3reno/usr/src/contrib/rcs/src/READ_ME |server=FTP server |url-status=dead |title=CSRG/cd2/4.3reno/usr/src/contrib/rcs/src/READ_ME |date=27 February 1989 }}</ref><!-- Better source needed -->

Ca. 1989, the RCS license was altered to something similar to the contemporary [[BSD licenses#Previous license|BSD licenses]], as seen by comments in the source code.<ref>{{Cite FTP |url=ftp://ftp.mrynet.com/operatingsystems/CSRG/cd2/4.3reno/usr/src/contrib/rcs/src/rcs.c |server=FTP server |url-status=dead |title=CSRG/cd2/4.3reno/usr/src/contrib/rcs/src/rcs.c |date=15 August 1989}}</ref><!-- Better source needed -->

{{quote|Redistribution and use in source and binary forms are permitted provided that the above copyright notice and this paragraph are duplicated in all such forms and that any documentation, advertising materials, and other materials related to such distribution and use acknowledge that the software was developed by Walter Tichy.}}

RCS 4.3, released 26 July 1990, was distributed "under license by the [[Free Software Foundation]]", under the terms of the [[GNU General Public License|GPL]].<ref>RCS 4.3 README file.</ref>{{full citation needed|date=January 2022}}

OpenBSD provides a different implementation called ''OpenRCS'', which is BSD-licensed.<ref>{{Cite web |title=rcs(1) - OpenBSD manual pages |url=https://man.openbsd.org/rcs.1#HISTORY |access-date=2024-09-05 |website=man.openbsd.org}}</ref>