push @{ $machinearray{$machine} }, $pwline;

##</code><code>##

    my %machines = (
        machine1 => {
            user1 => 'pwline1',
            user2 => 'pwline2',
        },

        machine2 => {
            user1 => 'pwline1',
            user3 => 'pwline3',
        },
    );

##</code><code>##

    if (!exists $machines{$machine}{$uname}) {
        ## User doesn't exist. Add him/her.
        $machines{$machine}{$uname} = $pwline;
    }