use XML::Simple ':strict';  # since example code doesn't have
                            # backward-compatibility issues
use DBX;
use strict;   # of course!
use warnings; 

my $config  = XMLin "config.xml";  # XML left as an exercise to the reader
my $driver  = $config->{driver};
my $connstr = $config->{connection_string};
my $SQL     = $config->{query};

my $conn = DBX->$driver($connstr, "", "");

my $rs = $conn->query($SQL);

while($rs) {
    print $rs->field("client") . "\n";
    $rs->field("client", "test");
    $rs->move_next;
}