trim in new php version, but i have old php

[searain]

$mystring=trim($mystring, ",");

this trim is in 4.1, but i have php4.0, how can i have the codes to do the same trim as

$mystring=trim($mystring, ","); in the new php 4.1.

[the_Igel]

$mystring = preg_replace('/[\s,]$/', '', $mystring);