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RCSINTRO(1)                                                        RCSINTRO(1)

       rcsintro - introduction to RCS commands

       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 fre-
       quently, 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
       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 colleagues.

       o      Resolve access conflicts.  When two or more programmers wish  to
              modify  the  same  revision, RCS alerts the programmers and pre-
              vents 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  accord-

   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  descrip-
       tion.   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  exam-
       ple, 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  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.  Turn-
       ing 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 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 num-
       ber  the subsequent revisions with 2.2, 2.3, etc.  The corresponding co

              co  -r2  f.c     and     co  -r2.1  f.c

       retrieve the latest revision numbered 2.x and the revision 2.1, respec-
       tively.   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  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


       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 fol-

              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 mod-
       ules 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 identi-
       fication markers; see co(1) for details.

       Author: Walter F. Tichy.
       Manual Page Revision: 1.5; Release Date: 1999/08/27.
       Copyright (C) 1982, 1988, 1989 Walter F. Tichy.
       Copyright (C) 1990, 1991, 1992, 1993 Paul Eggert.

       ci(1), co(1), ident(1), rcs(1), rcsdiff(1),  rcsintro(1),  rcsmerge(1),
       Walter  F. Tichy, RCS--A System for Version Control, Software--Practice
       _ Experience 15, 7 (July 1985), 637-654.

GNU                               1999/08/27                       RCSINTRO(1)


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