It is not part of the TCP standard, to check whether the peer is still alive, or whether the connection is still there. The TCP conncections are only maintained "locally".

connected() can not be used to check the availability of peer, or the status of connection.

However for Perl socket programs, when the peer closes the connection, you would reach eof of the socket, just as a normal file does.

This demo shows how the socket reaches eof, when yahoo closes the connection after the transmission is done: 
use strict;
use IO::Socket;

my $yahoo = IO::Socket::INET->new(Proto => "tcp",
                                   PeerPort => 80,
                                   PeerAddr => "www.yahoo.com",
                                   Timeout => 2000)
             || die "failed to connect\n";
my $req = "GET / HTTP/1.1\r\nHost: www.yahoo.com\r\n\r\n";
print $yahoo $req;
my $count = 0;
while (<$yahoo>) {
    print "packet count = ", ++ $count, ", and first 20 chars of the p
+acket = ", substr($_, 0, 20), "\n";
}

[download]

In reply to Re: Simple TCP Server to output data by pg
in thread Simple TCP Server to output data by gnu@perl

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