<?php

$input = "\t\n\r \tfoo";

    function lspace($input) {
        if ($input && ($input = strval($input))) {
            if (preg_match('/^\s*/', $input, $matches)) {
                return $matches[0];
            }
        }
        return '';
    }

var_dump(lspace("foo"));
var_dump(lspace("  foo"));
var_dump(lspace("  \t  foo"));
var_dump(lspace("\n  \tfoo"));