rcsintro - introduction to RCS commands
The Revision Control System (RCS) manages multiple revi-
sions of files. RCS automates the storing, retrieval,
logging, identification, and merging of revisions. RCS is
useful for text that is revised frequently, for example
programs, documentation, graphics, papers, and form let-
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.
Functions of RCS
- Store and retrieve multiple revisions of text. RCS
saves all old revisions in a space efficient way.
Changes no longer destroy the original, because the
previous revisions remain accessible. Revisions
can be retrieved according to ranges of revision
numbers, symbolic names, dates, authors, and
- Maintain a complete history of changes. RCS logs
all changes automatically. Besides the text of
each revision, RCS stores the author, the date and
time of check-in, and a log message summarizing the
change. The logging makes it easy to find out what
happened to a module, without having to compare
source listings or having to track down colleagues.
- Resolve access conflicts. When two or more pro-
grammers wish to modify the same revision, RCS
alerts the programmers and prevents one modifica-
tion from corrupting the other.
- Maintain a tree of revisions. RCS can maintain
separate lines of development for each module. It
stores a tree structure that represents the ances-
tral relationships among revisions.
- Merge revisions and resolve conflicts. Two sepa-
rate lines of development of a module can be coa-
lesced by merging. If the revisions to be merged
affect the same sections of code, RCS alerts the
user about the overlapping changes.
- Control releases and configurations. Revisions can
be assigned symbolic names and marked as released,
stable, experimental, etc. With these facilities,
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configurations of modules can be described simply
- Automatically identify each revision with name,
revision number, creation time, author, etc. The
identification is like a stamp that can be embedded
at an appropriate place in the text of a revision.
The identification makes it simple to determine
which revisions of which modules make up a given
- Minimize secondary storage. RCS needs little extra
space for the revisions (only the differences). If
intermediate revisions are deleted, the correspond-
ing deltas are compressed accordingly.
Getting Started with RCS
Suppose you have a file f.c that you wish to put under
control of RCS. If you have not already done so, make an
RCS directory with the command
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 oth-
ers are called working files. To get back the working
file f.c in the previous example, use the check-out com-
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
co -l f.c
You can now edit f.c.
Suppose after some editing you want to know what changes
that you have made. The command
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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
ci error: no lock set by your name
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,
rcs -l f.c
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
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
rcs -U f.c and rcs -L f.c
If you don't want to clutter your working directory with
RCS files, create a subdirectory called RCS in your work-
ing 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
To avoid the deletion of the working file during check-in
(in case you want to continue editing or compiling),
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ci -l f.c or ci -u f.c
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 use-
ful if you want to continue editing, the second one if you
just want to read the file. Both update the identifica-
tion 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.
ci -r2 f.c or ci -r2.1 f.c
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
co -r2 f.c and co -r2.1 f.c
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 revi-
sion with a number consisting of two fields. Numbers with
more than two fields are needed for branches. For exam-
ple, to start a branch at revision 1.3, invoke
ci -r1.3.1 f.c
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).
RCS can put special strings for identification into your
source and object code. To obtain such identification,
place the marker
into your text, for instance inside a comment. RCS will
replace this marker with a string of the form
$Id: filename revision date time author state
With such a marker on the first page of each module, you
can always see with which revision you are working. RCS
keeps the markers up to date automatically. To propagate
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the markers into your object code, simply put them into
literal character strings. In C, this is done as follows:
static char rcsid = "$Id$";
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 pro-
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 identi-
fication markers; see co(1) for details.
Author: Walter F. Tichy.
Manual Page Revision: 1.1; Release Date: 1996/08/12.
Copyright (C) 1982, 1988, 1989 Walter F. Tichy.
Copyright (C) 1990, 1991, 1992, 1993 Paul Eggert.
ci(1), co(1), ident(1), rcs(1), rcsdiff(1), rcsintro(1),
Walter F. Tichy, RCS--A System for Version Control,
Software--Practice & Experience 15, 7 (July 1985),
GNU 1996/08/12 5
Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.