use strict;

my @cat = qw( cat );
my ( $in_q, $out_q, $err_q );

use IPC::Run qw( start pump finish timeout );

# Incrementally read from / write to scalars.  Note that $in_q
# is a queue that is drained as it is used. $h is for "harness".
my $h = start \@cat, \$in_q, \$out_q, \$err_q, timeout(10), debug => 1;

$in_q .= "some input\n";
pump $h until $out_q =~ /input\n/g;

$in_q .= "some more input\n";
pump $h until $out_q =~ /\G.*more input\n/;

$in_q .= "some final input\n";
finish $h or die "cat returned $?";

warn $err_q if $err_q;
print $out_q ;    ## All of cat's output