NAME
rcsintro - introduction to RCS commands
DESCRIPTION
programs, documentation, graphics, papers, and form letters. 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
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(5).
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.
Manual Page Revision: ; Release Date: .
Copyright © 1982, 1988, 1989 Walter F. Tichy.
Copyright © 1990, 1991, 1992, 1993 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.