Go for Event!

It's ugly, unfactor'd, but works.

use Event;
use IO::File;

my $f = IO::File->new('for t in 1 2 3 4;do echo one $t; sleep 4;done; 
+|');
my $g = IO::File->new('for t in 1 2 3 4;do echo two $t; sleep 4;done; 
+|');
my $h = IO::File->new('for t in 1 2 3 4;do echo three $t; sleep 4;done
+; |');
my (@f,@g,@h);

my $done;

sub newIO {
  my ($f,$fr) = @_;
  Event->io(
    fd => $f,
    poll => 're',
    cb => sub {
      my $e = $_[0];
      my $w = $e->w;
      my $fd = $w->fd;
      if ($fd->eof) {
          $pending--;
          $w->cancel;
          return;
      }
      my $line = <$fd>;
      push @{$fr}, $line;
      },
  );
  $pending++;
}
Event->idle(
    min => 1, max => 2,
    cb => sub {
        print "last one: $f[-1]";
        print "last two: $g[-1]";
        print "last three: $h[-1]";
        Event::unloop if ($pending == 0);
    },
);
newIO($f,\@f);
newIO($g,\@g);
newIO($h,\@h);
Event::loop;
print @f;
print @g;
print @h;
[download]

Gives:

last one: one 1
last two: two 1
last three: three 1
last one: one 1
last two: two 1
last three: three 1
last one: one 1
last two: two 1
last three: three 1
last one: one 2
last two: two 2
last three: three 2
last one: one 2
last two: two 2
last three: three 2
last one: one 2
last two: two 2
last three: three 2
last one: one 2
last two: two 2
last three: three 2
last one: one 3
last two: two 3
last three: three 3
last one: one 3
last two: two 3
last three: three 3
last one: one 3
last two: two 3
last three: three 3
last one: one 3
last two: two 3
last three: three 3
last one: one 4
last two: two 4
last three: three 4
last one: one 4
last two: two 4
last three: three 4
last one: one 4
last two: two 4
last three: three 4
last one: one 4
last two: two 4
last three: three 4
last one: one 4
last two: two 4
last three: three 4
one 1
one 2
one 3
one 4
two 1
two 2
two 3
two 4
three 1
three 2
three 3
three 4