my $pat = qr/\w+ ((w)hite|(b)lack)/;

    $_ = 'mostly black';
    print "$1 starts with $+\n" if /$pat/;

    $_ = 'but some white spaces';
    print "$1 starts with $+\n" if /$pat/;

##</code><code>##

    my $pat = qr/\w+ ((w)hit(e)|(b)lac(k))/;

    $_ = 'mostly black';
    my($word, $first, $last) = grep defined $_, /$pat/;
    print "$word starts with $first and ends with $last\n" if $word;

    $_ = 'but some white spaces';
    ($word, $first, $last) = grep defined $_, /$pat/;
    print "$word starts with $first and ends with $last\n" if $word;

##</code><code>##

    my $pat = qr/\w+ ((w)hit(e)|(b)lac(k))/;
    $str = 'mostly black but some white spaces';
    while ($str =~ /$pat/g) {
        my @m = get_captures($str);
        print "$m[1] starts with $m[2] and ends with $m[3]\n";
    }

    sub get_captures {
        map { defined $+[$_] 
                ? substr($_[0],$-[$_],$+[$_]-$-[$_]) 
                :()
            } 0..$#+;
    }