Exploring Expect

Enabling Internal Diagnostics

In long scripts, it is convenient to be able to turn Expect’s internal diagnostics off. You can do this with the command "exp_internal 0“. You can use the exp_internal command to turn the diagnostics off and on as you like. For example, it is common to surround just a small group of commands or even one command with exp_internal commands as you narrow down where the problem lies in a script.

exp_internal 1
expect
exp_internal 0

You may also find it convenient to conditionalize the use of exp_internal. For example, you can set a global variable that controls whether all of the exp_internal commands are actually executed. The following code permits "exp_internal 1" commands in the code to execute only when the variable debug_enable is nonzero. The idea is that this variable is set once—which is much easier than adding or commenting in and out commands scattered throughout a script. (In Chapter 9 (p. 219), I will describe how to get this effect on a script-wide basis without changing the script at all.)

if $debug_enable {exp_internal 1}
expect . . .
exp_internal 0
send . . .
expect . . .
if $debug_enable {exp_internal 1}
send . . .
expect . . .
exp_internal 0

The "exp_internal 0" commands do not have to be conditionalized. It is not an error to execute "exp_internal 0" even if diagnostics have not been enabled. In this case, "exp_internal 0" is just ignored.

An even more convenient way to control diagnostic output is to define procedures such as the following ...