C programmers often include debugging code in #ifdef DEBUG / #endif sections. By compiling with -DDEBUG the code gets included, otherwise it's left out. So the debugging code can be (and often is) left in, for future use.

WIBNI you could do the same in Perl? Source filters (see Filter and Filter::Simple) can obviously do the same; the Filter distribution even includes an example of doing this.

Here's a lighter-weight version. Unfortunately, it does leave an empty sub when debugging is disabled.

Usage

Save the snippet in a file Debug.pm and stow the file somewhere useable.

Add use Debug (1); to the start of your code. Put debugging code in a block, preceded by DEBUG:

use Debug (1);

print "This is the program\n";
DEBUG { print "Debugging mode is ON\n"; };
print "Program continues...\n";
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To turn off the debugging portions, chance "use Debug (1)" to plain "use Debug".

If you need more than one type of debugging block, add another argument to use Debug:

use Debug (1);
use Debug (0, DBG_SPECIAL);

DEBUG { warn "First type\n"; };
DBG_SPECIAL { warn "Second type\n"; }
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# This goes in Debug.pm...
package Debug;
use strict;


sub doit (&) {
  my $cref = shift;
  $cref->();
}

sub dontdoit (&) {}

# Export appropriate one as DEBUG

sub import {
  shift;
  my $package = caller || '';
  my $name = $_[1] || 'DEBUG';
  {
    no strict 'refs';
    * { "${package}::$name" } =
      (@_ && $_[0]) ? \&doit : \&dontdoit;
  }
}

1;
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