[Expectperl-discuss] How not to receive my own STDOUT?

[Kilian A. F. <fo...@in...>]

I'm trying to fool a proprietary program into thinking it is talking
to a terminal when it is really talking to another program. Here is a
minimal version to show my problem:

#!/usr/bin/env perl
use warnings;
use strict;
use Expect;

our $pid = Expect->spawn("cat") or die "Couldn't spawn, $!";
$pid->log_stdout(0);

sub read_output($ ) {
  my $s = shift;
  
  my @comm = $pid->expect(1,'-re',"$s");
  (print "Error.", return 0) if $comm[1];
  (print "No answer.", return 0) unless defined $comm[2];

  (my $answer = $comm[2]) =~ s/\r/<NL>/;
  print "received `$answer'!\n";
  return 1;
}

$pid->send("Hi there.\n");

while(read_output("^.+")){
  # do nothing
};

I expect the output:

received `Hi there.<NL>'!

But I get:

received `Hi there.<NL>'!
received `Hi there.<NL>'!

Why is ->expect reading my own STDOUT? How can I make it stop?