Hey now, 21 years after this inspired module was added, I just wanted to note a small bug in the Filter subroutine (in package Filter::Handle). It should be:

    sub Filter {
      my $fh = shift;
      tie *{ $fh }, __PACKAGE__, @_;
    }
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Note how the subroutine UnFilter uses the shift correctly. Also, it's a shame that this is no longer on CPAN. But this chunk of module is enough to put into one's "private" library for use. Using a CODE reference, you can duplicate all your STDOUT and STDERR (including any that comes out of perl warnings), like the following:

    select STDERR; $|=1;
    select STDOUT; $|=1;
    use FileHandle;
    my $LOG_FH = new FileHandle($logfile, "w");
    $LOG_FH->autoflush;

    open(DUPOUT, ">&STDOUT") or die "Couldn't dup STDOUT: $!\n";
    open(DUPERR, ">&STDERR") or die "Couldn't dup STDERR: $!\n";

    use Filter::Handle qw/subs/;
    our $FILTER_STDOUT = sub 
    { local $_ = "@_";
      print DUPOUT $_; 
      sprintf "[STDOUT]: %s", "@_"
        if (defined $LOG_FH && $LOG_FH->opened);
    };  
    our $FILTER_STDERR = sub 
    { local $_ = "@_";
      print DUPERR $_; 
      sprintf "[STDERR]: %s", "@_"
        if (defined $LOG_FH && $LOG_FH->opened);
    };  
    
    ## Call Filter to tie the filehandles
    ## Call UnFilter to untie the filehandles (don't care)
    Filter \*STDOUT, $LOG_FH, $FILTER_STDOUT;
    Filter \*STDERR, $LOG_FH, $FILTER_STDERR;
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I like this much better than IO::Tee, because I don't need a custom filehandle to print to to get a logfile of all output. I'm continuing to play around with this and may update this thread more later.