4.3BSD-UWisc/man/catl/rcsintro.l
RCSINTRO(1) UNIX Programmer's Manual RCSINTRO(1)
NAME
rcsintro - introduction to RCS commands
DESCRIPTION
The Revision Control System (RCS) manages multiple revisions
of text files. RCS automates the storing, retrieval, log-
ging, identification, and merging of revisions. RCS is use-
ful for text that is revised frequently, for example pro-
grams, documentation, graphics, papers, form letters, etc.
The basic user interface is extremely simple. The novice
only needs to learn two commands: _c_i and _c_o. _C_i, short for
"checkin", 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. _C_o, short for
"checkout", 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, sym-
bolic 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
checkin, 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 pro-
grammers wish to modify the same revision, RCS alerts
the programmers and prevents one modification from cor-
rupting 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.
o+ Release and configuration control. Revisions can be
assigned symbolic names and marked as released, stable,
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experimental, etc. With these facilities, configura-
tions of modules can be described simply and directly.
o+ Automatic identification of each revision with name,
revision number, creation time, author, etc. The iden-
tification is like a stamp that can be embedded at an
appropriate place in the text of a revision. The iden-
tification 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 correspond-
ing deltas are compressed accordingly.
Getting Started with RCS
Suppose you have a file f.c that you wish to put under con-
trol of RCS. Invoke the checkin 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 checkin 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
checkout 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
_C_i increments the revision number properly. If _c_i complains
with the message
ci error: no lock set by <your login>
then your system administrator has decided to create all RCS
files with the locking attribute set to `strict'. In this
case, you should have locked the revision during the previ-
ous checkout. Your last checkout should have been
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co -l f.c
Of course, it is too late now to do the checkout with lock-
ing, because you probably modified f.c already, and a second
checkout 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 CHECKIN by anybody but the locker.
If your RCS file is private, i.e., if you are the only per-
son who is going to deposit revisions into it, strict lock-
ing is not needed and you can turn it off. If strict lock-
ing is turned off, the owner off the RCS file need not have
a lock for checkin; 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 checkin (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 impli-
cit checkout. The first form also locks the checked in revi-
sion, the second one doesn't. Thus, these options save you
one checkout operation. The first form is 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 _c_i the number you want assigned to a checked in
revision. Assume all your revisions were numbered 1.1, 1.2,
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1.3, etc., and you would like to start release 2. The com-
mand
ci -r2 f.c or ci -r2.1 f.c
assigns the number 2.1 to the new revision. From then on,
_c_i will number the subsequent revisions with 2.2, 2.3, etc.
The corresponding _c_o commands
co -r2 f.c and co -r2.1 f.c
retrieve the latest revision numbered 2.x and the revision
2.1, respectively. _C_o 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 _r_c_s_f_i_l_e(5).
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 _i_d_e_n_t extracts such markers from any file, even
object code and dumps. Thus, _i_d_e_n_t lets you find out which
revisions of which modules were used in a given program.
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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 checkin. Thus, you can
maintain the complete history of your file directly inside
it. There are several additional identification markers;
see _c_o(1) for details.
IDENTIFICATION
Author: Walter F. Tichy, Purdue University, West Lafayette,
IN, 47907.
Revision Number: 3.0 ; Release Date: 83/05/11 .
Copyright 8c9 1982 by Walter F. Tichy.
SEE ALSO
ci(1), co(1), ident(1), merge(1), rcs(1), rcsdiff(1),
rcsmerge(1), rlog(1), rcsfile(5).
Walter F. Tichy, "Design, Implementation, and Evaluation of
a Revision Control System," in _P_r_o_c_e_e_d_i_n_g_s _o_f _t_h_e _6_t_h _I_n_t_e_r_-
_n_a_t_i_o_n_a_l _C_o_n_f_e_r_e_n_c_e _o_n _S_o_f_t_w_a_r_e _E_n_g_i_n_e_e_r_i_n_g, IEEE, Tokyo,
Sept. 1982.
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