rcsintro(1) DG/UX R4.11 rcsintro(1)
NAME
rcsintro - introduction to RCS commands
DESCRIPTION
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, documentation,
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, symbolic names, dates, authors, and states.
· 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 programmers wish
to modify the same revision, RCS alerts the programmers and
prevents one modification 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 ancestral relationships 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 overlapping changes.
· Control releases and configurations. Revisions can be
assigned symbolic names and marked as released, stable,
experimental, etc. With these facilities, configurations of
modules can be described simply and directly.
· 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
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 control of
RCS. If you have not already done so, make an RCS directory with the
command
mkdir RCS
Then invoke the check-in command
ci f.c
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 others are
called working files. To get back the working file f.c in the
previous example, use the check-out command
co f.c
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
rcsdiff f.c
tells you the difference between the most recently checked-in version
and the working file. You can check the file back in by invoking
ci f.c
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, invoke
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 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 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 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. The command
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 1.3.1.1 to the new revision. For more information about
branches, see rcsfile(4).
Automatic Identification
RCS can put special strings for identification into your source and
object code. To obtain such identification, place the marker
$Id$
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.
IDENTIFICATION
Author: Walter F. Tichy.
Revision Number: 1995/08/01; Release Date: 16:09:02.
Copyright © 1982, 1988, 1989 by Walter F. Tichy.
Copyright © 1990, 1991 by Paul Eggert.
SEE ALSO
ci(1), co(1), ident(1), rcs(1), rcsdiff(1), rcsintro(1), rcsmerge(1),
rlog(1)
Walter F. Tichy, RCS--A System for Version Control, Software
--Practice & Experience 15, 7 (July 1985), 637-654.
Licensed material--property of copyright holder(s)