Exploring Expect

Timing Out

The special timeout pattern matches after a given amount of time. Unlike the expect command, the timeout pattern does not depend on the timeout variable. Instead, the timeout is given after the keyword itself. The timeout is specified in seconds. The action follows the number of seconds. For example, the action in the interact command below is executed if the user presses no keys for more than an hour.

interact timeout 3600 {
    send_user "Idle for 1 hour - you are being logged out"
    return
}

In this example, the output of the spawned process is not timed. This is useful in preventing irrelevant system messages (”System going down at midnight.“) from making the session seem active.

The interact command uses explicitly specified timeouts so that you can use different timers simultaneously. For instance, the following fragment times out the user after 10 seconds and the spawned process after 600 seconds.

interact {
    timeout 10 {
        send_user "Keep typing -- we pay you by the character!"
    }
    -o
    timeout 600 {
        send_user "It's been ten minutes with no response.\
                   I recommend you go to lunch!"
    }
}

On many systems, the following script can be used to fake out shells that automatically exit after periods of inactivity. The script works by detecting the inactivity and sending a space and immediately removing it.

spawn $env(SHELL)
interact timeout 3000 {send " \177"}

As shown here, the script waits for a little less than an hour under the assumption that the spawned program’s timeout is exactly an ...