RCSINTRO(1) USER COMMANDS RCSINTRO(1)
rcsintro - introduction to RCS commands
The Revision Control System (RCS) manages multiple revisions
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, docu
mentation, graphics, papers, and form letters.
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, sym
bolic names, dates, authors, and states.
· Maintain a complete history of changes. RCS logs all
changes automatically. Besides the text of each revi
sion, 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 programmers
wish to modify the same revision, RCS alerts the pro
grammers and prevents one modification from corrupting
· Maintain a tree of revisions. RCS can maintain sepa
rate lines of development for each module. It stores a
tree structure that represents the ancestral relation
ships among revisions.
· Merge revisions and resolve conflicts. Two separate
lines of development of a module can be coalesced by
merging. If the revisions to be merged affect the same
sections of code, RCS alerts the user about the over
· Control releases and configurations. Revisions can be
assigned symbolic names and marked as released, stable,
experimental, etc. With these facilities, configura
tions of modules can be described simply and directly.
· Automatically identify each revision with name, revi
sion number, creation time, author, etc. The identifi
cation is like a stamp that can be embedded at an
appropriate place in the text of a revision. The iden
tification makes it simple to determine which revisions
of which modules make up a given configuration.
· Minimize secondary storage. RCS needs little extra
space for the revisions (only the differences). If
intermediate revisions are deleted, the corresponding
deltas are compressed accordingly.
Getting Started with RCS
Suppose you have a file f.c that you wish to put under con
trol 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 summa
rize the changes that you made.
Files in the RCS directory are called RCS files; the others
are called working files. To get back the working file f.c
in the previous example, use the check-out command
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
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 locker.
If your RCS file is private, i.e., if you are the only per
son who is going to deposit revisions into it, strict lock
ing is not needed and you can turn it off. If strict lock
ing 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 working
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 intelligently.)
To avoid the deletion of the working file during check-in
(in case you want to continue editing or compiling), invoke
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 useful
if you want to continue editing, the second one if you just
want to read the file. Both update the identification mark
ers 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. The com
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 revision with
a number consisting of two fields. Numbers with more than
two fields are needed for branches. For example, 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 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 program.
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 identification
markers; see co(1) for details.
Author: Walter F. Tichy.
Manual Page Revision: 5.3; Release Date: 1993/11/03.
Copyright © 1982, 1988, 1989 Walter F. Tichy.
Copyright © 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), 637-654.
GNU Last change: 1993/11/03 1