export DEBUGGING=1
perl -Mbegin yourscript.pl

##</code><code>##

perl -Mbegin=VERBOSE yourscript.pl

##</code><code>##

perl -Mbegin=all yourscript.pl

##</code><code>##

======= yourscript.pl ===================

# code that's always compiled and executed

=begin DEBUGGING

warn "Only compiled and executed when DEBUGGING or 'all' enabled\n"

=cut

# code that's always compiled and executed

=begin VERBOSE

warn "Only compiled and executed when VERBOSE or 'all' enabled\n"

=cut

# code that's always compiled and executed

========================================

##</code><code>##

my $foo = 2;

=begin DEBUGGING

my $foo = 1;
warn "debug foo = $foo\n";

=cut

warn "normal foo = $foo\n";

##</code><code>##

my $foo = 2;

{

my $foo = 1;
warn "foo = $foo\n";

}

warn "normal foo = $foo\n";