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
      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 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
           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 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.
      If you have not already done so, make an RCS directory with the

           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 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 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.
      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 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 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,

           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

           $Id$ into your text, for instance inside a comment.  RCS will
           replace this marker with a string of the form

           $Id$ 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.


      Author: Walter F. Tichy.
      Manual Page Revision: 1.3; Release Date: 1996/01/31.
      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.