GNU Screen has a 'stuff' command.
        http://www.gnu.org/software/screen/manual/screen.html#index-stuff-165

This can be used to "inject" new keystrokes into the current PTY.

What I'd LIKE to do is make it so that running programs could tell Screen to add some characters to
its input queue.

As an example, a script could 1) tell Screen to add the specified password to the input-buffer, and
then 2) start up `ssh username@site`.

This is effectively like using Expect, BUT:
        1) I use lots of machines all over, many of them that don't have Expect already
        2) this method doesn't require creating or re-routing any new PTYs



One way to do this is to patch the code to trigger off of something like the ANSI print command:
        http://www.gnu.org/software/screen/manual/screen.html#Printcmd