Using keywords
==============

   To include a keyword string you simply include the relevant text
string, such as `$Id$', inside the file, and commit the file.  CVS will
automatically expand the string as part of the commit operation.

   It is common to embed `$Id$' string in the C source code.  This
example shows the first few lines of a typical file, after keyword
substitution has been performed:

     static char *rcsid="$Id: samp.c,v 1.5 1993/10/19 14:57:32 ceder Exp $";
     /* The following lines will prevent `gcc' version 2.X
        from issuing an "unused variable" warning. */
     #if __GNUC__ == 2
     #define USE(var) static void * use_##var = (&use_##var, (void *) &var)
     USE (rcsid);
     #endif

   Even though a clever optimizing compiler could remove the unused
variable `rcsid', most compilers tend to include the string in the
binary.  Some compilers have a `#pragma' directive to include literal
text in the binary.

   The `ident' command (which is part of the RCS package) can be used
to extract keywords and their values from a file.  This can be handy
for text files, but it is even more useful for extracting keywords from
binary files.

     $ ident samp.c
     samp.c:
          $Id: samp.c,v 1.5 1993/10/19 14:57:32 ceder Exp $
     $ gcc samp.c
     $ ident a.out
     a.out:
          $Id: samp.c,v 1.5 1993/10/19 14:57:32 ceder Exp $

   SCCS is another popular revision control system.  It has a command,
`what', which is very similar to `ident' and used for the same purpose.
Many sites without RCS have SCCS.  Since `what' looks for the
character sequence `@(#)' it is easy to include keywords that are
detected by either command.  Simply prefix the RCS keyword with the
magic SCCS phrase, like this:

     static char *id="@(#) $Id: ab.c,v 1.5 1993/10/19 14:57:32 ceder Exp $";