empty - run processes and applications under pseudo-terminal (PTY) sessions and replace TCL/Expect with a simple shell-tool

empty is an utility that provides an interface to execute and/or interact with processes under pseudo-terminal sessions (PTYs). This tool is definitely useful in programming of shell scripts designed to communicate with interactive programs like telnet, ssh, ftp, etc. In some cases empty can be the simplest replacement for TCL/expect or other similar programming tools because empty:

• can be easily invoked directly from shell prompt or script
• does not use TCL, Perl, PHP, Python or anything else as an underlying language
• is written entirely in C
• has small and simple source code
• can easily be ported to almost all UNIX-like systems

Nowadays empty was successfully compiled and tested on:

Installation is simple: download, then ungzip and untar the source code:

	tar zxvf empty-x.y.z.tgz

If you have Linux or *BSD just run:

	make all install clean

on any other *NIX try:

	make `uname -s` all install clean

	 or

	make `uname -s`-gcc all install clean

This will compile and place empty with its manual page under /usr/local tree. Good luck and beware of bugs!

empty was written by Mikhail E. Zakharov on the basic idea of pty-4.0 Copyright (c) 1992, Daniel J. Bernstein, but no code was ported from it.

Great thanks to:

• Aleksey Kozlov - avtolik@newmail.ru
• Alexey Rudometov - rudometov@u-systems.ru
• Alex Slyotov - aslyotov@gmail.com
• Bernd Schuller
• David Hofstee - davidh@blinker.nl
• Dennis Schridde
• Dmitry S. Vlasov - vlasov@quantum.ru
• Elisender - allex_9@ngs.ru
• Lang Qiu - qiulang@gmail.com
• Ralf Winkel
• Roman Gorohov - idle@idle.org.ru
• sdio - sdio4lor @ gmail.com
• Sergey Redin - sergey@redin.info
• Sergey V - flexdsl@mail.ru
• Sergey Yaroshevsky - astraserg@proc.ru
• Sylvain DEGUT - sylvain.degut@neuf.fr
• Vincenzo Maggio - vince.maggio@gmail.com

I express deep gratitude to Hewlett Packard AO Russia and personally to Denis Karzhavin and Andrew Kuchinsky for C110 (9000/777) workstation

#!/bin/sh

empty -f -i in -o out telnet foo.bar.com
empty -w -i out -o in "ogin:" "luser\n"
empty -w -i out -o in "assword:" "TopSecret\n"
empty -s -o in "who am i\n"
empty -s -o in "exit\n"

#!/usr/bin/expect

spawn telnet foo.bar.com 
expect ogin {send luser\r}
expect assword {send TopSecret\r}
send "who am i\r" 
send "exit\r"
expect eof

#!/usr/bin/perl

use Expect;

my $exp = Expect->spawn("telnet foo.bar.com");
$exp->expect($timeout,
        [ 'ogin: $' => sub {
                     $exp->send("luser\n");
                     exp_continue; }
        ],

        [ 'assword:$' => sub {
                      $exp->send("TopSecret\n");
                      exp_continue; }
        ],
        '-re', qr'[#>:] $'
);
$exp->send("who am i\n");
$exp->send("exit\n");
$exp->soft_close();

#!/usr/local/bin/python

import pexpect

child = pexpect.spawn('telnet foo.bar.com');

child.expect('ogin: ');
child.sendline('luser');

child.expect('assword:');
child.sendline('TopSecret');

child.sendline('who am i');
child.sendline('exit');

child.expect(pexpect.EOF);

print child.before;

All the examples above show the same quick telnet session using empty and various scripting languages.