RCSINTRO(1L) 1983 RCSINTRO(1L)
NAME
rcsintro - introduction to RCS commands
DESCRIPTION
The Revision Control System (RCS) manages multiple
revisions of text 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, form letters, etc.
The basic user interface is extremely simple. The novice
only needs to learn two commands: ci(1L) and co(1L). Ci,
short for "check in", deposits the contents of a text file
into an archival file called an RCS file. An RCS file
contains all revisions of a particular text file. Co,
short for "check out", retrieves revisions from an RCS
file.
Functions of RCS
o Storage and retrieval of 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 Maintenance of 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.
o Resolution of 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 Maintenance of 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 Merging of revisions and resolution of 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.
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o Release and configuration control. 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 Automatic identification of 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 Minimization of 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. Invoke the check-in command
ci f.c
This command creates the RCS file f.c,v, 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 ending in ,v are called RCS files (`v' stands for
`versions'), 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 f.c,v and
writes it into f.c. You can now edit f.c and check it back
in by invoking
ci f.c
Ci increments the revision number properly. If ci
complains with the message
ci error: no lock set by <your login>
then your system administrator has decided to create all
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RCS files with the locking attribute set to `strict'. In
this case, you should have locked the revision during the
previous check-out. Your last check-out should have been
co -l f.c
Of course, it is too late now to do the check-out with
locking, because you probably modified f.c already, and a
second 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 3 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), 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
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useful if locking is strict, the second one if not strict.
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 2 fields. Numbers
with more than 2 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(5L).
Automatic Identification
RCS can put special strings for identification into your
source and object code. To obtain such identification,
place the marker
$Header$
into your text, for instance inside a comment. RCS will
replace this marker with a string of the form
$Header: filename revision_number 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[] = "$Header$";
The command ident extracts such markers from any file,
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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(1L) for details.
IDENTIFICATION
Author: Walter F. Tichy, Purdue University, West
Lafayette, IN, 47907.
Revision Number: 1.2 ; Release Date: 89/05/02 .
Copyright (C) 1982, 1988, 1989 by Walter F. Tichy.
SEE ALSO
ci(1L), co(1L), ident(1L), merge(1L), rcs(1L),
rcsdiff(1L), rcsmerge(1L), rlog(1L), rcsfile(5L),
Walter F. Tichy, "Design, Implementation, and Evaluation
of a Revision Control System," in Proceedings of the 6th
International Conference on Software Engineering, IEEE,
Tokyo, Sept. 1982.
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