Exploring Expect

The -D Flag

The -D flag enables a debugger that is described in more detail in Chapter 18 (p. 406), so I will just explain the flag very briefly here. "-D" takes a boolean argument describing whether to start the debugger or to just initialize it so that the debugger can be started at a later time (such as by a command or by pressing ^C).

Here is an example that starts the debugger so that you get interactive control before the first command in script is executed.

% expect -D 1 script

Arguments to the left of the -D are processed before starting the debugger. Arguments to the right are processed after starting the debugger. Consider the following command:

% expect -c "set a 1" -D 1 -c "set b 2"
1: set b 2
dbg1.1>

In this example, Expect evaluated "set a 1" and then started the debugger. The debugger shows that the next command to be executed is "set b 2" and then interactively prompts for a command.