function get_filename() {
$array = debug_backtrace();
$file = basename( $array[0]['file'] );
echo '<!-- ' . $file . ' -->' . "\n";
}
<style>
li { float: left; margin: 1em; }
li:nth-child(2n+1) { clear: both; }
</style>
<ul>
<li> 1
<li> 2
<li> 3
<li> 4
<li> 5
<li> 6
</ul>
