use strict;
    use warnings;
    use Data::Dumper;
    use Config;
    use re 'eval';

    my %ARGV;
    my $string = q{It is --now 12:34};

    # Mimic Getopt::Euclid's generated regex to process a --now command line
    # option.
    $string =~ s{(??{exists $ARGV{WHEN} })
            --now\s+(\d+:\d+)(?{$ARGV{WHEN} = $^N})
        }{thyme}xsm;

    print "Perl $Config{version} on $Config{osname}:\n",
        Data::Dumper->Dump( [ \%ARGV, $string ], [qw(ARGV string)] );

    exit 0;

##</code><code>##

    : 2009-02-10 19:56:05 (C:/Perl510/bin/perl regex_test.pl)
    Perl 5.10.0 on MSWin32:
    $ARGV = {
            'WHEN' => '12:34'
            };
    $string = 'It is thyme';

    : 2009-02-10 19:56:05 (perl regex_test.pl)
    Perl 5.10.0 on cygwin:
    $ARGV = {
            'WHEN' => undef
            };
    $string = 'It is thyme';