Define (Debugging with GDB)
23.1.1 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 an unlimited number of arguments separated by whitespace. Arguments are accessed within the user command via
$arg0…$argN. A trivial example:
define adder print $arg0 + $arg1 + $arg2 end
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.
$argc may be used to find out how many arguments have been passed.
define adder if $argc == 2 print $arg0 + $arg1 end if $argc == 3 print $arg0 + $arg1 + $arg2 end end
Combining with the
eval command (see eval) makes it easier to process a variable number of arguments:
define adder set $i = 0 set $sum = 0 while $i < $argc eval "set $sum = $sum + $arg%d", $i set $i = $i + 1 end print $sum end
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 argument
commandname may be a bare command name consisting of letters, numbers, dashes, dots, and underscores. It may also start with any predefined or user-defined prefix command. For example, ‘
define target my-target’ creates a user-defined ‘
target my-target’ command.
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
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.
Define or mark the command
commandname as a user-defined prefix command. Once marked,
commandname can be used as prefix command by the
define command. Note that
define-prefix can be used with a not yet defined
commandname. In such a case,
commandname is defined as an empty user-defined command. In case you redefine a command that was marked as a user-defined prefix command, the subcommands of the redefined command are kept (and GDB indicates so to the user).
(gdb) define-prefix abc (gdb) define-prefix abc def (gdb) define abc def Type commands for definition of "abc def". End with a line saying just "end". >echo command initial def\n >end (gdb) define abc def ghi Type commands for definition of "abc def ghi". End with a line saying just "end". >echo command ghi\n >end (gdb) define abc def Keeping subcommands of prefix command "def". Redefine command "def"? (y or n) y Type commands for definition of "abc def". End with a line saying just "end". >echo command def\n >end (gdb) abc def ghi command ghi (gdb) abc def command def (gdb)
Used inside a user-defined command, this tells GDB that this command should not be repeated when the user hits RET (see repeat last command).
List all user-defined commands and all python commands defined in class COMMAND_USER. The first line of the documentation or docstring is included (if any).
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. This does not work for user-defined python commands.
The value of
max-user-call-depth controls how many recursion levels are allowed in user-defined commands before GDB suspects an infinite recursion and aborts the command. This does not apply to user-defined python commands.
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 GDB commands that normally print messages to say what they are doing omit the messages when used in a user-defined command.