rcsintro - phpMan

RCSINTRO(1) RCSINTRO(1)

NAME
rcsintro - introduction to RCS commands

DESCRIPTION
The Revision Control System (RCS) manages multiple revisions of files. RCS auto-
mates the storing, retrieval, logging, identification, and merging of revisions.
RCS is useful for text that is revised frequently, for example programs, documenta-
tion, 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 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 develop-
ment for each module. It stores a tree structure that represents the ances-
tral 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 facili-
ties, 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 con-
figuration.

· Minimize secondary storage. RCS needs little extra space for the revisions
(only the differences). If intermediate revisions are deleted, the corre-
sponding 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 revi-
sion 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 work-
ing 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 subdi-
rectory 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 con-
tinue 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 sub-
sequent 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 high-
est 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 com-
ment. 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.

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 1993/11/03 RCSINTRO(1)

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