Just print to the socket. Here's an example:

#!/usr/bin/perl

use strict;
use warnings;

use IO::Socket;

my $sock = IO::Socket::INET -> new (LocalAddr => "localhost:5000",
                                    Listen    =>  5) or die $!;

while (my $child = $sock -> accept ()) {
    my $line = <$child>;
    print $child "You send: $line";
    close $child;
}
__END__
[download]

Start it, and from another window:

$ telnet localhost 5000
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Hello!
You send: Hello!
Connection closed by foreign host.
$
[download]

Abigail