--- gets([rs])
--- readline([rs])

    Ruby 󥿥ץ꥿¹Ի˰ȤͿ줿ե(ʤɸ
    )ĤʤŪʥե(Ȥ߹ѿ $<
     ARGF ǥǤ) ɤ߹ǡʸ֤
    եνãˤ nil ֤ޤ

    Ԥζڤϰ rs ǻꤷʸˤʤޤrs 
    ǥեͤȤ߹ѿ $/ ͤǤɤ߹
    ʸȤ߹ѿ $_ ˤ⥻åȤޤ

    rs  nil ꤹȹԶڤʤȤߤʤƥեƤ
    ٤ɤ߹ߤޤ
    ʸ "" ꤹϢ³ԤԤζڤȤߤʤޤ
    (ѥ饰ե⡼)

    readline  gets ƱƯ򤷤ޤ
    եκǸޤɤ㳰 EOFError ȯޤ

