use IPC::Run qw ( start pump finish )
## Build the harness, open all pipes, and launch the subprocesses

my $h = start  \@cat, \$in, \$out ;
$in = "first input\n" ;

## Now do I/O.  start() does no I/O.
pump $h while length $in ;  ## Wait for all input to go

## Now do some more I/O.
$in = "second input\n" ;
pump $h until $out =~ /second input/ ;

## Clean up
finish $h or die "cat returned $?" ;