# 2.11BSD#431 - /usr/new/man/cat1/rcsintro.0

    RCSINTRO(1L)	    UNIX Programmer's Manual	     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, 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: 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 con-
         tains 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, 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
    	  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 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 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 RCS
         files with the locking attribute set to `strict'. In this
         case, you should have locked the revision during the previ-
         ous check-out. Your last check-out should have been

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    	       co  -l  f.c

         Of course, it is too late now to do the check-out with lock-
         ing, 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 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 of the RCS file need not have a
         lock for check-in; all others still do. Turning strict lock-
         ing 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 impli-
         cit 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
         locking is strict, the second one if not strict.  Both
         update the identification markers in your working file (see
         below).

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         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 com-
         mand

    	       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, even
         object code and dumps.  Thus, ident 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 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: 87/02/27 .
         Copyright (C) 1982 by Walter F. Tichy.

    SEE ALSO
         ci(1L), co(1L), ident(1L), merge(1L), rcs(1L), rcsdiff(1L),
         rcsmerge(1L), rlog(1L)
         Walter F. Tichy, "Design, Implementation, and Evaluation of
         a Revision Control System," in Proceedings of the 6th Inter-
         national Conference on Software Engineering, IEEE, Tokyo,
         Sept. 1982.

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