Exploring Expect

Using kibitz From Other Expect Scripts

In the previous chapter, I described kibitz, a script that allows two users to control a common process. kibitz has a -noproc flag, which skips starting a common process and instead connects together the inputs and outputs of both users. The second user will receive what the first user sends and vice versa.

By using -noproc, a disconnected script can use kibitz to communicate with a user. This may seem peculiar, but it is quite useful and works well. The disconnected script plays the part of one of the users and requires only a few lines of code to do the work.

Imagine that a disconnected script has reached a point where it needs to contact the user. You can envision requests such as "I need a password to continue” or "The 3rd backup tape is bad, replace it and tell me when I can go on“.

To accomplish this, the script simply spawns a kibitz process to the appropriate user. kibitz does all the work of establishing the connection.

spawn kibitz -noproc $user

Once connected, the user can interact with the Expect process or can take direct control of one of the spawned processes. The following Expect fragment, run from cron, implements the latter possibility. The variable proc is initialized with the spawn id of the errant process while kibitz is the currently spawned process. The tilde is used to return control to the script.

spawn some-process; set proc $spawn_id . . . . . . # script now has question or problem so it contacts user spawn kibitz -noproc ...