Apologies. Here's a version that eliminates much of the extra stuff, and adds a bunch of comments:

#!/usr/bin/env perl

use strict;
use warnings;

use Time::HiRes qw(usleep);
use IO::Select;
use File::Spec::Functions qw(catfile);

use constant USLEEP_TIME => 25_000; # Microseconds
use constant RUN_TIME    => 30;     # Seconds

my $cmd = catfile((getpwnam($ENV{USER}))[7],'scripts','outputter'); # 
+This just sets up the path to the external script.
print "Our command is >>>$cmd<<<\n";

open my $r, '-|', $cmd or die $!;       # Open a pipe to read output f
+rom a command.
my $s = IO::Select->new($r);            # Create an IO::Select object 
+on our pipe's filehandle, $r.
my $pinged = 0;                         # Poor-man's messaging: We hav
+en't received a ping yet.
my $start = time();                     # Record our start time so we 
+can calculate when to exit.

while(time() < $start + RUN_TIME) {     # Iterate until we run out of 
+time.
    if    ($r->eof) {                   # Finish if the target command
+ has finished all output and termianted.
        last;
    }
    elsif ($s->can_read(0)) {               # See if there's something
+ available to read.
        chomp(my $i = <$r>);                # Read from our pipe and c
+homp.
        print "\n<$i>\n";                   # Print what we read.
        $pinged = 1 if $i eq 'ping';        # Send a message that we r
+ead something.
    }
    elsif ($pinged) {                       # If we have a ping messag
+e, print a pong.
        print "(pong)\n";
        $pinged = 0;                        # And unset the message.
    }
    else {
        usleep USLEEP_TIME;                 # If there's nothing to do
+, sleep briefly.
        print '.';                          # Print something to let e
+veryone know we're thinking of them.
        STDOUT->flush;
    }
}                                           # lather, rinse, repeat.
[download]

Again, the "outputter" script (terribly named) should be:

#!/usr/bin/env perl

use strict;
use warnings;
use IO::Handle;

STDOUT->autoflush(1);
while (1) {
    print STDOUT "ping\n";
    sleep 2;
}
[download]

The output is going to look approximately like this:

Our command is >>>/home/......./scripts/outputter<<<
......................................................................
+..........
<ping>
(pong)
......................................................................
+..........
<ping>
(pong)
.................................^C
Command terminated
[download]

If I had let it run long enough it would time out and exit cleanly.

++davido for your keen and kleen explanation!

The future reader can be also interested in throttling something with ularm

L*

There are no rules, there are no thumbs..
Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.