- preg_replace: documentation ( source)
<?php
$re = '/([$][a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*+)/m';
$str = '"SELECT * FROM table WHERE admin=\'".$admin."\' AND id=".$idclient." AND something=".$something;';
$subst = 'functionname($1)';
$result = preg_replace($re, $subst, $str);
echo $result;