Your problem appears to be the range that you are using - instead of using a character range you're trying to match against an invalid '2-5' + 5'.

Instead use '[0-9]+' to match against one or more numerical digits.

The following code matches against your input:

my $input = "netaddr   10.1.4.43   Internet Address   True";
my $ipaddress = "unknown";

if ( $input =~ /([0-9]+\.[0-9]+\.[0-9]+\.[0-9]+)/ )
{
    $ipaddress = $1;
}


print $ipaddress . "\n";
[download]