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20.1 User-defined Commands

A user-defined command is a sequence of No value for GDBN commands to which you assign a new name as a command. This is done with the define command. User commands may accept up to 10 arguments separated by whitespace. Arguments are accessed within the user command via $arg0…$arg9. A trivial example:

define adder
  print $arg0 + $arg1 + $arg2

To execute the command use:

adder 1 2 3

This defines the command adder, which prints the sum of its three arguments. Note the arguments are text substitutions, so they may reference variables, use complex expressions, or even perform inferior functions calls.

In addition, $argc may be used to find out how many arguments have been passed. This expands to a number in the range 0…10.

define adder
  if $argc == 2
    print $arg0 + $arg1
  if $argc == 3
    print $arg0 + $arg1 + $arg2
define commandname

Define a command named commandname. If there is already a command by that name, you are asked to confirm that you want to redefine it.

The definition of the command is made up of other No value for GDBN command lines, which are given following the define command. The end of these commands is marked by a line containing end.

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.


Used inside a user-defined command, this tells No value for GDBN that this command should not be repeated when the user hits <RET> (see section repeat last command).

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 No value for GDBN commands used to define commandname (but not its documentation). If no commandname is given, display the definitions for all user-defined commands.

show max-user-call-depth
set max-user-call-depth

The value of max-user-call-depth controls how many recursion levels are allowed in user-defined commands before No value for GDBN suspects an infinite recursion and aborts the command.

In addition to the above commands, user-defined commands frequently use control flow commands, described in Command Files.

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 No value for GDBN commands that normally print messages to say what they are doing omit the messages when used in a user-defined command.

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