Sorry that aint necessarily so. Here is some trivial code that does the teletype thing. The client(s) have no way to disconnect BTW, that is left as an exercise for the reader yada yade.

#!/usr/bin/perl
$|++;
use IO::Socket;
use IO::Select;
my $lsn = IO::Socket::INET->new( 
    Listen    => 10,
    LocalAddr => 'localhost',
    LocalPort => 9000
);
my $client = new IO::Select( $lsn );
while( my @ready = $client->can_read ) {
    for my $fh (@ready) {
        if($fh == $lsn) {
            warn "Accepted new socket\n";
            my $new = $lsn->accept;
            $client->add($new);
        }
        else {
            # process socket
            sysread($fh, $_, 1 );
            print;   # NB syswrite(STDOUT,$_,1) will be unbuffered by 
+default
        }
    }
}
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Note that sysread bypasses STDIO and all buffering. Read will sort of buffer (newlines only in this one byte reading config). I never use recv so really have NFI what it does.

I've tried it on my system, and it gets inside the while loop only when a newline character is send to the server. $client->can_read returns only when a newline character is received. I tried telnet and netcat as clients. It turns out the problem is not with sysread or recv but can_read. Thanks.