Instead, I'm getting:

command: cd hello
command: cd world
response:
command: cd goodbye
...

##</code><code>##

sub sendData {
  my $request = $_[0];
  $responseData = ""; #class member var
  print SOCKET "$request\n" . "\000" or die "print SOCKET: $!";
  
  $responseData = <SOCKET>;
  ...
  print "resp: $responseData\n";
}

##</code><code>##

  $responseData = ""; #class member var