--- ~ self

    self ɽ˥ѥ뤷ơȤ߹ѿ $_ Ф
    ޥåԤޥå֤Υǥå֤ޤ
    $_ =~ self ƱǤ

    $_ ʸǤʤ nil ֤ޤ

    ruby 1.7 feature:
       $_ =~ Regexp.compile(Regexp.quote(self))
    ƱǤ

