# This is cat.pl
while(<>) {
  print;
}

##</code><code>##

# This is ls.pl
use strict;
use warnings;
use IPC::Open2;
# $^X is the path to my Perl
open2(*OUTPUT,*INPUT,"$^X", "cat.pl") or die "$!";
print INPUT "first line\nsecond line\n";
close INPUT;
my @result=<OUTPUT>;
close OUTPUT;
print "RESULT:\n@result\n";

##</code><code>##

perl ls.pl

##</code><code>##

RESULT:
first line
 second line