#!/usr/bin/perl -l

use strict;
use warnings;
use Tie::Scalar::Timeout;

tie my $line, 'Tie::Scalar::Timeout',
  EXPIRES => '+1s', POLICY => undef;

$line = system("whoami");

while (defined($_ = $line)) {
    foreach $line(my @lines) {
        print "$_" or die $@;
    }
}