You could try:

#! perl -slw
use strict;
use Data::Dumper;
use DBI;

my $dbh = DBI->connect('dbi:WMI:');

my $sth = $dbh->prepare(<<WQL);
    SELECT * FROM Win32_SerialPort
WQL

$sth->execute();

while (my( $serial ) = $sth->fetchrow) {
    print Dumper $serial;
}
[download]

I can't confirm if it works, because I just discovered that this machine doesn't have any serial ports!

I guess if I ever need one, I'd have to buy a USB-serial adapter.

A crude way of getting an available port is to just sequentially attempt to open them until you get one that succeeds. Start at 0 and count up to 9 ( I do recall there are some tricks to win32 com ports over 9, but I doubt you have more than 9 going :-)

#! perl -slw
use strict;
use Win32::TieRegistry 0.20;

# open registry node
my $key= new Win32::TieRegistry "LMachine\\Hardware\\DEVICEMAP\\SERIAL
+COMM\\";

# Get list of value names:
my @valueNames= $key->ValueNames;

foreach my $item (@valueNames)
{
    my $valueString= $key->GetValue($item);
    print $valueString."\n";
}
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