gistfile1.php

<?php

$str[] = ':[email protected] PRIVMSG #test_channel :test message';
$str[] = ':[email protected] PRIVMSG #test_channel :fii message';
$str[] = ':[email protected] PRIVMSG #test_channel :foo message';
$str[] = ':[email protected] PRIVMSG #test_channel :message test boo';
$str[] = ':[email protected] PRIVMSG #test_channel :blaat fii message';

foreach($str as $s) {
    preg_match('/:([^!]+)[^:]+:(.*(test|fii).*)/', $s, $matches);
    print_r( $matches );
}