HP gnu source-level debugger 5992-4701 - Manual (Page 288)

are executed repeatedly as long as the expression
evaluates to true.
document commandname Document the user-defined command commandname,
so that it can be accessed by help. The command
commandname
must already be defined. This
command reads lines of documentation just as define
reads the lines of the command definition, ending
with end. After the document command is finished,
help on command commandname displays the
documentation you have written.
You may use the document command again to change
the documentation of a command. Redefining the
command with define does not change the
documentation.
help user-defined List all user-defined commands, with the first line of
the documentation (if any) for each.
show user, show user
commandname Display the GDB commands used to define
commandname
(but not its documentation). If no
commandname is given, display the definitions for
all user- defined commands.
When user-defined commands are executed, the commands of the definition are not
printed. An error in any command stops execution of the user-defined command.
If used interactively, commands that would ask for confirmation proceed without
asking when used inside a user-defined command. Many GDB commands that normally
print messages to say what they are doing omit the messages when used in a
user-defined command.
18.2 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, and treat them normally
during normal execution, you could define:
define hook-stop
handle SIGALRM nopass
end
define hook-run
handle SIGALRM pass
288 Canned Sequences of Commands