3.9)  How do I run 'passwd', 'ftp', 'telnet', 'tip' and other interactive
      programs from a shell script or in the background?

      These programs expect a terminal interface.  Shells makes no
      special provisions to provide one.  Hence, such programs cannot
      be automated in shell scripts.

      The 'expect' program provides a programmable terminal interface
      for automating interaction with such programs.  The following
      expect script is an example of a non-interactive version of
      passwd(1).

        # username is passed as 1st arg, password as 2nd
        set password [index $argv 2]
        spawn passwd [index $argv 1]
        expect "*password:"
        send "$password\r"
        expect "*password:"
        send "$password\r"
        expect eof

      expect can partially automate interaction which is especially
      useful for telnet, rlogin, debuggers or other programs that have
      no built-in command language.  The distribution provides an
      example script to rerun rogue until a good starting configuration
      appears.  Then, control is given back to the user to enjoy the game.

      Fortunately some programs have been written to manage the
      connection to a pseudo-tty so that you can run these sorts of
      programs in a script.

      To get expect, email "send pub/expect/expect.shar.Z" to
      library@cme.nist.gov or anonymous ftp same from
      ftp.cme.nist.gov.

      Another solution is provided by the pty 4.0 program, which runs a
      program under a pseudo-tty session and was posted to
      comp.sources.unix, volume 25.  A pty-based solution using named
      pipes to do the same as the above might look like this:

        #!/bin/sh
        /etc/mknod out.$$ p; exec 2>&1
        ( exec 4<out.$$; rm -f out.$$
        <&4 waitfor 'password:'
            echo "$2"
        <&4 waitfor 'password:'
            echo "$2"
        <&4 cat >/dev/null
        ) | ( pty passwd "$1" >out.$$ )

      Here, 'waitfor' is a simple C program that searches for
      its argument in the input, character by character.

      A simpler pty solution (which has the drawback of not
      synchronizing properly with the passwd program) is

        #!/bin/sh
        ( sleep 5; echo "$2"; sleep 5; echo "$2") | pty passwd "$1"