Exploring Expect

An Extended Example—xkibitz

This section covers an extended example: xkibitz. xkibitz is similar in effect to kibitz but works in a very different way. This script uses indirect spawn ids to be added and dropped dynamically. The script also draws together a number of other concepts including interacting with an xterm and handling a SIGWINCH.

xkibitz uses xterms to give multiple users the same view of a shell (or any application). The xterms provide a vehicle for easy interhost communication. xkibitz does I/O with remote hosts by spawning an xterm with the display set appropriately. By doing so, the script avoids having to deal with passwords, remote logins, or proxy servers. Interhost communication comes free because X provides it along with an authentication mechanism. This will become more meaningful as I walk through the script.

The script starts by defining a help procedure which just prints a message. The message lists the commands that can be used once the program starts. The "+" command adds a display. The "-" drops a display. The "=" lists the displays. And "return" returns xkibitz to usual user-application interaction.

When a display is added, it is given a tag—a small integer that allows the user an easier means of identifying a display than the display name itself which can be very long.

#!/usr/local/bin/expect -- proc help {} { puts "commands meaning" puts "-------- -------" puts "return return to program" puts "= list" puts "+ <display> add" puts "- <tag> drop" puts "where ...