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GNU 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, identifi-
cation, and merging of revisions. RCS is useful for text that is
revised frequently, for example programs, documentation, graph-
ics, 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 par-
ticular file. co, short for "check out", retrieves revisions
from an RCS file.
Functions of RCS
o 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.
o 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 col-
leagues.
o 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.
o 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.
o 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.
o 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.
o 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.
o 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 con-
tents 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 some-
body 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 direc-
tory, 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 infor-
mation 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 revi-
sions 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 c 1982, 1988, 1989 Walter F. Tichy.
Copyright c 1990, 1991, 1992, 1993 Paul Eggert.
(NOTE from TA: These links aren't working very well. Just use man.)
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.