A cool thing that you can do with gdb is to change the values of variables in programs that are already running, or calling their functions. For example you can update a variable on your parent shell, e.g., "export" the variable $X to your parent (!) :

    gdb --batch-silent -ex "attach $PPID" -ex "call (int)bind_variable(\"X\",\"$X\",0)"

I confess that I use this trick in my shell scripts more than strictly necessary, just for fun.