x12345:

This is a bit oversimplified, as there's insufficient error checking and such. But I'd suggest doing something like "terminate the loop if I haven't received anything for X seconds" (where you'd have to choose X to balance between performance, and the possibility of a false failure). You could start with something like this:

my $timeout = time+$X;  # timeout if we don't see anything in $X secon
+ds
my $ttl_bytes_rcvd=0;   # haven't received anything yet
while (time < $timeout) {
   ... read the data ...

   if ($bytes_read>0) {
      $timeout = time+$X; # Reset timeout if we actually saw some data
      $ttl_bytes_rcvd += $bytes_read;
   }

   # don't just hammer the CPU, give other processes a chance to do so
+mething,
   # as well as allowing a bit of time for more data to arrive
   sleep 0.5;
}
if ($ttl_bytes_rcvd) {
   # process successful response
   ...
}
else {
   die "Error!  No data received!\n";
}
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...roboticus

When your only tool is a hammer, all problems look like your thumb.

You could check whether you closed your session and don't expect any more data. Maybe eof could help there too.

Using these two criteria, you should be able to determine whether there was just not anything read, or whether the other end has closed the connection.