I couldn't help thinking a PerlIO layer would be more appropriate, so I wrote a layer: 
use v5.8.0;
use strict;
use warnings;

package PerlIO::via::TimeStamp;

sub PUSHED {
   my ($class, $mode, $fh) = @_;

   # We can't be the bottom layer.
   if (@_ < 3) {
      # XXX Set "$!"?
      return -1;
   }

   # We only support writting.
   if ($mode ne 'w' && $mode ne 'a') {
      # XXX Set "$!"?
      return -1;
   }

   return bless({ nl => 1 }, $class);
}

sub WRITE {
   my  $self              =  $_[0];
   our $ibuf; local *ibuf = \$_[1];
   my  $fh                =  $_[2];

   return 0 if not length $ibuf;

   local ($,, $\);

   our $nl; local *nl = \($self->{nl});
   my $lt;

   my $qsep = quotemeta($/);
   while ($_[1] =~ /((?:(?!$qsep).)*(?:($qsep)|(?!$qsep).))/gs) {
      my $obuf = '';

      if ($nl) {
         $lt ||= "[" . localtime() . "] ";
         $obuf .= $lt;
      }

      $obuf .= $1;
      print $fh $obuf
         or return 0;

      $nl = !!$2;
   }
  
   return length($ibuf);
}

1;

[download]
binmode(STDOUT, '>:via(TimeStamp)');
print("test\n");

[download]

Untested.

In reply to Re^3: Un "tie"ing a "tie" by ikegami
in thread Un "tie"ing a "tie" by herby1620

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