use warnings;
use strict;

my $password = "hide_me";
my $log_file = "test.log";
open STDOUT, "| perl | tee -a $log_file";
select STDOUT;
$| = 1;

print '
  use warnings;
  use strict;
  select STDOUT;
  $| = 1;
  my $chr;
  $_ = "";
  while ($chr = getc DATA) {
      $_ .= $chr;
      next unless $chr =~ /\s/;
      s/' . (quotemeta $password) . '/removed/ig;
      print;
      $_ = "";
  }
  print;
  __DATA__
';

print "The password is $password\n";
foreach (qw{Output is unbuffered if these words are printed one at a time.}) {
        print $_, " ";
        select undef, undef, undef, 0.3;
}
print "\n";
foreach (split //, "Even one character at a time: $password should be filtered.\n") {
        print;
        select undef, undef, undef, 0.1;
}
close STDOUT;

##</code><code>##

The password is removed
Output is unbuffered if these words are printed one at a time.
Even one character at a time: removed should be filtered.