--- ~ self

    self ɽ˥ѥ뤷ơȤ߹ѿ $_ Ф
    ޥåԤޥå֤Υǥå֤ޤ
    $_ =~ Regexp.compile(self) ƱǤ

    $_ ʸǤʤ nil ֤ޤ

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

    ruby 1.8 feature: Υ᥽åɤλѤϿ侩ޤ(ٹ
    Ϥޤ)ˡRegexp#= [Regexp/~] ʤɤѤƤ
    

