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

my @commands = ( 'sleep 3 && find /usr/share/doc',
                 'sleep 4 && find /opt',
                 'sleep 5 && df' );

my @fhs;
for my $i (0 .. $#commands) {
    open $fhs[$i], '-|', $commands[$i] or die "Can't run $commands[$i]";
}

for my $i (0 .. $#commands) {
    print "=== $commands[$i] ===\n";
    print while readline $fhs[$i];
}