Debugging with GDB

Node:Define, Next:Hooks, Up:Sequences

### User-defined commands

A user-defined command is a sequence of GDB 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.

`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 GDB command lines, which are given following the `define` command. The end of these commands is marked by a line containing `end`.

`if`
  Takes a single argument, which is an expression to evaluate. It is followed by a series of commands that are executed only if the expression is true (nonzero). There can then optionally be a line `else`, followed by a series of commands that are only executed if the expression was false. The end of the list is marked by a line containing `end`.
`while`
  The syntax is similar to `if`: the command takes a single argument, which is an expression to evaluate, and must be followed by the commands to execute, one per line, terminated by an `end`. The commands are executed repeatedly as long as the expression evaluates to true.
`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.

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

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 GDB commands that normally print messages to say what they are doing omit the messages when used in a user-defined command.