[php] How do I remove a comma off the end of a string?

i guess you're concatenating something in the loop, like

foreach($a as $b)
  $string .= $b . ',';

much better is to collect items in an array and then join it with a delimiter you need

foreach($a as $b)
  $result[] = $b;

$result = implode(',', $result);

this solves trailing and double delimiter problems that usually occur with concatenation