my %hash = ( hello => "foo", world => "bar");
my $hashref = \%hash;       # store a reference to the %hash
print $hashref->{hello};    # prints "foo"
$hashref->{world} = "quz";  # change "bar" to "quz" in orig. hash

##</code><code>##

my $DEBUG = 0;  # at the top of the program
...
$DEBUG and print Dumper(...);
# or
print Dumper(...) if $DEBUG;

##</code><code>##

use constant DEBUG => 0;
...
DEBUG and print Dumper(...);