Nonblocking, nondestructible test for waiting data on TTYs, sockets and probably pipes
# $Header: /CVSROOT/keypressed/DESCRIPTION,v 1.1 2008-05-30 16:59:00 tino Exp $
#
# $Log: DESCRIPTION,v $
# Revision 1.1  2008-05-30 16:59:00  tino
# First try
#

<ul>
<li> Returns 0 (true) if there is input data waiting. </li>
<li> Returns 1 if no input data waiting. </li>
<li> Returns 255 on errors. </li>
<li> Return is undefined on unknown input types. </li>
<li> Does not read or print anything. </li>
<li> Does not set tty into CBREAK mode!  As the tty usually is in line mode you need to press Enter for keypressed to detect the input </li>
</ul>

Example 1:
<pre>while ! keypressed; do ...; done</pre>

Example 2:
<pre>while ! keypressed </dev/tty; do ...; done</pre>

Limitations and bugs:
<ul>
<li> The input data is not touched and stays there to be read </li>
<li> Commandline is ignored for now </li>
<li> Only fd0 (stdin) is checked, be sure to use poper IO redirection <li>
<li> No Hangup detection </li>
<li> Works only on input types which support certain ioctl() and select(), known to work on TTYs and Sockets and maybe Pipes. </li>
<li> Behavior on unsupported types (files, non-tty devices, often Pipes) therefor is undefined.  It depends on your OS if select() signals read (gives true) or not (gives false) or error (gives 2). </li>
</ul>

This Works is placed under the terms of the Copyright Less License,
see file COPYRIGHT.CLL.  USE AT OWN RISK, ABSOLUTELY NO WARRANTY.

Actually this only is a minimum wrapper around a library call.