User-defined command hooks
==========================

   You may define *hooks*, which are a special kind of user-defined
command.  Whenever you run the command `foo', if the user-defined
command `hook-foo' exists, it is executed (with no arguments) before
that command.

   In addition, a pseudo-command, `stop' exists.  Defining
(`hook-stop') makes the associated commands execute every time
execution stops in your program: before breakpoint commands are run,
displays are printed, or the stack frame is printed.

   For example, to ignore `SIGALRM' signals while single-stepping, but
treat them normally during normal execution, you could define:

     define hook-stop
     handle SIGALRM nopass
     end
     
     define hook-run
     handle SIGALRM pass
     end
     
     define hook-continue
     handle SIGLARM pass
     end

   You can define a hook for any single-word command in GDB, but not
for command aliases; you should define a hook for the basic command
name, e.g.  `backtrace' rather than `bt'.  If an error occurs during
the execution of your hook, execution of GDB commands stops and GDB
issues a prompt (before the command that you actually typed had a
chance to run).

   If you try to define a hook which does not match any known command,
you get a warning from the `define' command.