hektor ~ $ ./retest 
Perl 5.10.0 on darwin:
$ARGV = {
          'WHEN' => undef
        };
$string = 'It is thyme';

hektor ~ $ /usr/bin/perl retest 
Perl 5.8.8 on darwin:
$ARGV = {
          'WHEN' => '12:34'
        };
$string = 'It is thyme';
##</code><code>##

telemachus ~ $ perl testre 
Perl 5.10.0 on linux:
$ARGV = {
          'WHEN' => undef
        };
$string = 'It is thyme';

telemachus ~ $ /usr/bin/perl testre 
Perl 5.10.0 on linux:
$ARGV = {
          'WHEN' => '12:34'
        };
$string = 'It is thyme';