You need to use a pseudo-tty to solve this problem. IO::Pty is a fairly easy way to solve this. Here's an example: 
#!/usr/bin/perl -w

use strict;

use IO::Pty;

my $pty = IO::Pty->new
    or die "Pty error: $!\n";
my $slave = $pty->slave
    or die "Pty slave error: $!\n";

# Run cat with stdout on the PTY.
pipe(PIPEREAD,PIPEWRITE);
if (fork()==0)
{
  # Child
  close(PIPEWRITE);
  close($slave);
  close(STDOUT)
      or die "Couldn't close STDOUT: $!\n";
  open(STDOUT,">&".$pty->fileno)
      or die "Couldn't re-open STDOUT: $!\n";
  close(STDIN)
      or die "Couldn't close STDIN: $!\n";
  open(STDIN,"<&PIPEREAD")
      or die "Couldn't re-open STDIN: $!\n";
  exec("/bin/cat")
      or die "Couldn't exec /bin/cat: $!\n";
}

# Parent
close(PIPEREAD);
close($pty);

select(PIPEWRITE);
$|=1;
select(STDOUT);

warn "Parent running\n";

foreach my $val (1..10) {
  print PIPEWRITE "$val\n";
  $_ = <$slave>;
  print "$_";
}

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In reply to Re: How to change Open2 input buffering by sgifford
in thread How to change Open2 input buffering by thecap

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