use strict;
use warnings;

use Parse::RecDescent;

$::RD_ERRORS=1;
$::RD_WARN=1;
$::RD_HINT=1;
$::RD_TRACE=1;

open(Parse::RecDescent::ERROR, '>', 'errfile')
   or die("Can't redirect errors to file 'errfile': $!\n");

open(Parse::RecDescent::TRACE, '>', 'tracefile')
   or die("Can't redirect errors to file 'tracefile': $!\n");

Parse::RecDescent->new('parse:')->parse('');

##</code><code>##

>perl 659805a.pl
printing code (3018) to RD_TRACE

>type errfile
    Parse::RecDescent: Treating "parse:" as a rule declaration

>type tracefile
 1|  parse   |Trying rule: [parse]                  |
 1|  parse   |Trying production: []                 |
 1|  parse   |>>Matched production: []<<            |
 1|  parse   |>>Matched rule<< (return value:       |
  |          |[parse])                              |
 1|  parse   |(consumed: [])                        |

##</code><code>##

use strict;
use warnings;

use vars '$tracemsg';
use vars '$tracecontext';
use vars '$tracerulename';
use vars '$tracelevel';

open (TRACE, ">&STDERR");
format TRACE =
@>|@|||||||||@^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<|
$tracelevel, $tracerulename, '|', $tracemsg
  | ~~       |^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<|
              $tracemsg
.

$tracemsg      = 'tracemsg';
$tracecontext  = 'tracecontext';
$tracerulename = 'tracerulename';
$tracelevel    = 'tracelevel';
write TRACE;

open(TRACE, ">tracefile") or die;

$tracemsg      = 'tracemsg';
$tracecontext  = 'tracecontext';
$tracerulename = 'tracerulename';
$tracelevel    = 'tracelevel';
write TRACE;

##</code><code>##

>perl -v

This is perl, v5.8.8 built for MSWin32-x86-multi-thread
(with 25 registered patches, see perl -V for more detail)

Copyright 1987-2006, Larry Wall

Binary build 817 [257965] provided by ActiveState http://www.ActiveState.com
Built Mar 20 2006 17:54:25
...

>perl 659805b.pl
tr|tracerulen|tracemsg                              |

>type tracefile
tr|tracerulen|tracemsg                              |