how do i remove a comma off the end of a string?

Question

I want to remove the comma off the end of a string. As it is now i am using

$string = substr($string,0,-1);

but that only removes the last

Answer 1

I had a pesky "invisible" space at the end of my string and had to do this

 $update_sql=rtrim(trim($update_sql),',');

But a solution above is better

 $update_sql=rtrim($update_sql,', ');