I don't think I properly understand the "expect" utility.

While searching for a way to automate a build process that involves jar signing, I came across expect, and thought I could use it to supply a password to jarsigner (whether having a password in a shell script is a good idea I understand the risks of).

expect "Enter Passphrase for keystore:"

Instead of catching this, the jarsigner sat waiting at that line.

Am I completely misunderstanding the point of "expect" and if I am, what can I use to achieve this effect?