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Command syntax

A GDB command is a single line of input. There is no limit on how long it can be. It starts with a command name, which is followed by arguments whose meaning depends on the command name. For example, the command, step, accepts an argument which is the number of times to step, as in ‘step 5’. You can also use the step command with no arguments. Some command names do not allow any arguments.

GDB command names may always be truncated if that abbreviation is unambiguous. Other possible command abbreviations are listed in the documentation for individual commands. In some cases, even ambiguous abbreviations are allowed; for example, s is specially defined as equivalent to step even though there are other commands whose names start with s. You can test abbreviations by using them as arguments to the help command.

A blank line as input to GDB (using the Return key just once) means to repeat the previous command. Certain commands (for example, run) will not repeat this way; such commands have unintentional repetition which might cause trouble and which it is unlikely you want to repeat.

The list and x commands, when you repeat them with Return key actions, construct new arguments rather than repeating exactly as generated. This permits easy scanning of source or memory.

GDB can also use Return in another way: to partition lengthy output, in a way similar to the common utility, more (see Screen size). Since it is easy to use Return one too many times in this situation, GDB disables command repetition after any command that generates this sort of display.

Any text from a # to the end of the line is a comment; it does nothing. This is useful mainly in command files (see Command files).