Var substitution in SELECT statements

This works:
$res = $conn->exec("select cust, contact, user_name, email from $t where
user_name = a1a");

This doesn't:
$c = "a1a";
$res = $conn->exec("select cust, contact, user_name, email from $t where
user_name = $c");

and returns the error:
Attribute 'a1a' not found


How do you do var substitution with the Pg module in Perl?

--
Randy Perry
sysTame
Mac Consulting/Sales