Debugging with GDB Manual (5900-1473; WDB 6.2; January 2011)

Type a line containing just end to terminate the
commands.
To remove all commands from a breakpoint, type
commands and follow it immediately with end; that is,
give no commands.
With no bnum argument, commands refers to the last
breakpoint, watchpoint, or catchpoint set (not to the
breakpoint most recently encountered).
Pressing RET as a means of repeating the last GDB command is disabled within a
command-list.
You can use breakpoint commands to start your program up again. Simply use the
continue command, or step, or any other command that resumes execution.
Any other commands in the command list, after a command that resumes execution, are
ignored. This is because any time you resume execution (even with a simple next or
step), you may encounter another breakpoint―which could have its own command
list, leading to ambiguities about which list to execute. On Itanium systems, if there is a
return command in the command list, any command after the return command is
ignored.
If the first command you specify in a command list is silent, the usual message about
stopping at a breakpoint is not printed. This may be desirable for breakpoints that are
to print a specific message and then continue. If none of the remaining commands print
anything, you see no sign that the breakpoint was reached. silent is meaningful only
at the beginning of a breakpoint command list.
The commands echo, output, and printf allow you to print precisely controlled
output, and are often useful in silent breakpoints. See “Commands for controlled output”
(page 292).
For example, here is how you could use breakpoint commands to print the value of x
at entry to foo whenever x is positive.
break foo if x>0
commands
silent
printf "x is %d\n",x
cont
end
One application for breakpoint commands is to compensate for one bug so you can test
for another. Put a breakpoint just after the erroneous line of code, give it a condition to
detect the case in which something erroneous has been done, and give it commands to
assign correct values to any variables that need them. End with the continue command
so that your program does not stop, and start with the silent command so that no
output is produced. Here is an example:
5.1 Breakpoints 57