my $var = 'foo';

warn $var; # prints foo
by_val( $var );
warn $var; # prints foo
by_ref( \$var );
warn $var; # prints bar

sub by_ref{
  my $var_ref = shift;
  $$var_ref = 'bar';
}

sub by_val{
  my $var = shift;
  $var = 'bar';
}

##</code><code>##

perl -e 'split//,q{john hurl, pest caretaker}and(map{print @_[$_]}(join(q{},map{sprintf(qq{%010u},$_)}(2**2*307*4993,5*101*641*5261,7*59*79*36997,13*17*71*45131,3**2*67*89*167*181))=~/\d{2}/g));'