On an SGI, it is the Alt key. M- is equivalent to ESC , except that you don't release Meta before pressing the next key, which makes it easier and faster than ESC . Whenever your cursor is on one of these prompts you can enter a GDB command. All GDB commands can be abbreviated unless doing so renders them ambiguous. Most of the commonly used commands can be abbreviated to one character.
Arguments listed in brackets are optional.
With no arguments, this lists the command classes. If a class is specified, it will briefly describe commands in that class. If a command is specified, it will provide help on using that command. When you recompile your program, GDB ought to recognize that and reload the file next time you run it. If it doesn't, use the file command.