#!/usr/bin/perl 

use IO::Pty;

my $cmd = "scp";
my @args = ("-v", "big.tar",  "egilchri\@other_machine:");

&do_cmd ($cmd, @args);

sub do_cmd {
    my ($cmd,@args) = @_;
    my $pty = IO::Pty->new or die "can't make Pty: $!";
    defined (my $child = fork) or die "Can't fork: $!";
    return $pty if $child;

  POSIX::setsid();
    my $tty = $pty->slave;
    close $pty;

    STDIN->fdopen($tty,"<")      or die "STDIN: $!";
    STDOUT->fdopen($tty,">")     or die "STDOUT: $!";
    STDERR->fdopen(\*STDOUT,">") or die "STDERR: $!";
    close $tty;
    $| = 1;
    exec $cmd,@args;
    die "Couldn't exec: $!";
}
[download]

Yeah, it sounds like you are pretty close. Here is a snippet (from unknown origin) that may help get the output from the pty. Maybe you can figure out how to combine your scripts?

#!/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. 
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();
[download]

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I'm not really a human, but I play one on earth. flash japh