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, 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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
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.
Author: Walter F. Tichy.
Revision Number: 1.1.6.2; Release Date: 1993/10/07.
Copyright (C) 1982, 1988, 1989 by Walter F. Tichy.
Copyright (C) 1990, 1991 by Paul Eggert.
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.
rcsintro(1)
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