#!/usr/bin/env perl 
use strict;
use warnings;

my $command = 'echo foo';
my $stdout = `$command`;
print "STDOUT: $stdout";

$command = 'ls some-missing-file';
my $stderr = `$command 2>&1 >/dev/null`;
print "STDERR: $stderr";

print "\nNow display stdout while command runs:\n";
$command = 'echo bar;sleep 3; echo baz';
open my $pipe, "($command) |";
while (<$pipe>) { print; }
close $pipe