RCSINTRO(1) 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 effi-cient efficient
cient 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 sum-marizing summarizing
marizing 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 differ-ences). differences).
ences). 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 contents
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 over-write overwrite
write 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 modi-fication. modification.
fication. (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 opera-tion. operation.
tion. 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: 1.1; Release Date: 1999/04/23.
Copyright (C) 1982, 1988, 1989 Walter F. Tichy.
Copyright (C) 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.
GNU 1999/04/23 RCSINTRO(1)
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