use strict;
use warnings;
use IO::Socket::INET;

my $socket = IO::Socket::INET->new(
    LocalHost  => '127.0.0.1',
    LocalPort  => 43618,
    Type       => SOCK_STREAM,
    Listen     => 10,
    Reuse      => 1,
) or die "server: can't open socket over port 43618";

warn "server initialized\n";

while ( 1 ) {

    while (my $client = $socket->accept) {
        my $request = <$client>;
        chomp($request);
        next unless $request;
        warn "client pid: $request\n";

        # close() um zu testen wie der Client darauf reagiert
        close($client);
    }

}

close($socket);

use strict;
use warnings;
use IO::Socket::INET;

my $socket = IO::Socket::INET->new(
    PeerAddr => '127.0.0.1',
    PeerPort => 43618,
    Proto    => 'tcp',
    Type     => SOCK_STREAM,
) or die "client: can't connect to 127.0.0.1:43618";

warn "client connected to server\n";

while ( 1 ) {
    warn "send pid to server\n";
    eval { print $socket "$$\n" };
    last if $@;
    sleep 1;
}

warn "lost connection\n";
close($socket);

#> perl server.pl 
server initialized
client pid: 2270

#> perl client.pl 
client connected to server
send pid to server
send pid to server
send pid to server

$SIG{PIPE}='IGNORE';