<dd>an object containing the return code, and possibly <code>message</code>, <code>signal</code> properties.</dd>
</dl>
</li>
</ol>
<h3>Details</h3>
<p>By default uses the <code>exec</code> system call which calls the command, waits for it to complete, and then
returns the output. For example a successful command should have a return code of <code>{ code: 0 }</code>.</p>
<p>Optionally can use <code>spawn</code> instead, which returns the output from stdout and stderr
as the command runs, usually one line at a time. On completion it then returns an object
on the 3rd port. For example, a successful command should return <code>{ code: 0 }</code>.</p>
<p>Errors may return extra information on the 3rd port <code>msg.payload</code>, such as a <code>message</code> string,
<code>signal</code> string.</p>
<p>The command that is run is defined within the node, with an option to append <code>msg.payload</code> and a further set of parameters.</p>
<p>Commands or parameters with spaces should be enclosed in quotes - <code>"This is a single parameter"</code></p>
<p>The returned <code>payload</code> is usually a <i>string</i>, unless non-UTF8 characters are detected, in which
case it is a <i>buffer</i>.</p>
<p>The node's status icon and PID will be visible while the node is active. Changes to this can be read by the <code>Status</code> node.</p>
<h4>Killing processes</h4>
<p>Sending <code>msg.kill</code> will kill a single active process. <code>msg.kill</code> should be a string containing
the type of signal to be sent, for example, <code>SIGINT</code>, <code>SIGQUIT</code> or <code>SIGHUP</code>.
Defaults to <code>SIGTERM</code> if set to an empty string.</p>
<p>If the node has more than one process running then <code>msg.pid</code> must also be set with the value of the PID to be killed.</p>
<p>If a value is provided in the <code>Timeout</code> field then, if the process has not completed when the specified number of seconds has elapsed, the process will be killed automatically</p>
<p>Tip: if running a Python app you may need to use the <code>-u</code> parameter to stop the output being buffered.</p>