use strict;
use warnings;

use IO::Socket ();

my $listen_fh = IO::Socket->new(
    Domain    => IO::Socket::AF_INET(),
    Proto     => 'tcp',
    LocalAddr => '127.0.0.1',
    Listen    => 1,
) or die("Unable to create listening socket: $!$/");

print('Listening on port ', $listen_fh->sockport(), '.', $/);

my $client_fh = $listen_fh->accept()
or die("Unable to accept a connection: $!$/");

print('Accepted a connection from ', $client_fh->peerhost(), ':', $client_fh->peerport(), '.', $/);

while (<$client_fh>) {
   print $client_fh uc($_);
}

print('Connection closed by client or by error.', $/);