- array_map: documentation ( source)
- strpos: documentation ( source)
- implode: documentation ( source)
- explode: documentation ( source)
<?php
$var = "one, two , three = ?, four = 'val', five , six = 1, seven, eight = 'val' , nine";
echo implode(', ', array_map(function($x){
return strpos($x, '=') === false ? $x.' = ?' : $x;
}, array_map("trim", explode(',', $var))));