--- readlines([rs])

    ޥɥ饤ȤͿ줿ե(ʤɸ) 
    ʤŪʥե(ARGFɤ߹ǡ
    ƹԤǤȤƤ֤ޤ

    Ԥζڤϰ rs ǻꤷʸˤʤޤrs 
    ǥեͤȤ߹ѿ $/ ͤǤ

    rs  nil ꤹȹԶڤʤȤߤʤޤ
    ʸ "" ꤹϢ³ԤԤζڤȤߤʤޤ
    (ѥ饰ե⡼)

