How do I run 'passwd', 'ftp', 'telnet', 'tip' and other interactive
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.$$ p; exec 2>&1
( exec 4
echo "$2"
<&4 waitfor 'password:'
echo "$2"
<&4 cat >/dev/null
) | ( pty passwd "$1" >out.$$ )
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"
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