....see IPC3 buffer limit problem for an intersting trick you can use to clear the pipe in tough applications

also see How to use pty for both STDERR AND STDOUT in IPC::Run, while doing something different with each? and for a pty here is example code:

#!/usr/bin/perl -w
# Description: Fool a process into
# thinking that STDOUT is a terminal, when in fact
# it may be a file or a pipe. This can be useful
# with programs like ps and w on linux... which
# will trunc their output to the width of the
# terminal, and, if they cannot detect the terminal
# width, use a default 80 columns. Wouldn't it be
# nice to say "ps -aux | grep etcshadow", and get
# output that looks like when you just say "ps
# -aux"? Well, that's the idea.

#try ./pseudotty "xterm -e top"
#or  ./pseudotty top

use warnings;
use strict; 
use IO::Pty; 

die "usage: ptyexec command [args]\n" unless @ARGV;

my $pty = IO::Pty->new; 
my $slave = $pty->slave;
open TTY,"/dev/tty" or die "not connected to a terminal\n"; 
$pty->clone_winsize_from(\*TTY);
close TTY;

my $pid = fork(); die "bad fork: $!\n" unless defined $pid; 
if (!$pid) {
#  $slave->close();
  open STDOUT,">&=".$pty->fileno() or die $!;
  exec @ARGV;
}else{
  $pty->close();
     while (defined (my $line = <$slave>)) {
       print $line;
     }
}

#cleanup pty for next run
$pty->close();
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