How to access postresql from within perl script

postgres_in_perl.pl

#!/usr/bin/env perl
# yum -y install perl-DBD-Pg

use DBI;
use warnings;

$HOST    = 'localhost';
$NAME    = 'db';
@USER_RO = ('readonly', 'guest');

$db = DBI->connect ("DBI:Pg:dbname=$NAME;host=$HOST", $USER_RO[0], $USER_RO[1])
           or die "unable to open database", DBI->errstr;

$query = $db->prepare ("SELECT * FROM get_testcases (?)");

$query->execute ('441147');
if ($query->rows)
{
        while (@fields = $query->fetchrow_array)
        {
                print join (":", @fields), "\n";
        }
}

$db->disconnect;