18 Canned Sequences of Commands

In addition to breakpoint commands (see “Breakpoint command lists” (page 61)), GDB provides the following two ways to store sequence of commands for execution as a unit:

•user-defined commands

•command files

18.1User-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. The following example illustrates the use of canned sequence of commands:

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 further functions calls.

The following constructs can be used to create canned sequence of commands:

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).

 

The if clause can be followed by an optional else

 

clause. You can add a list of commands to the else

 

clause which get executed only if the expression is

 

false.

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

18.1 User-defined commands 287