SOAP Server
<?php
class filesystem {
    function ls($dir)
    {
        return shell_exec("ls ".escapeshellarg($dir));
    }
}

// SOAP
$server = new SoapServer("urn:Object");
$server->setClass('filesystem');
$server->handle();
?>
SOAP Client
<?php
    $client = new SoapObject("http://example.com/server.php", "urn:Object");
    echo $client->ls("/vmlinuz*");
?>