use Errno ; # for ECONNREFUSED
use IO::Socket::INET ;

# portions copies from the IO::Socket::INET man page:
            $sock = IO::Socket::INET->new(PeerAddr => 'www.perl.org',
                                          PeerPort => 'http(80)',
                                          Proto    => 'tcp');

if( $sock == undef && $! == ECONNREFUSED ) {
    # server not operating?
}