--- sysread(length)
--- sysread(length[, buf])      ruby 1.7 feature

    read(2) [manual page] ѤϤԤʤϤ줿ǡ
    ޤʸ֤ޤեνãˤ㳰 
    EOFError ȯޤstdio ͳʤΤ 
    gets  getc  eof? ʤɤȺѤȻפư
    򤹤뤳Ȥޤ

    ǡɤ߹ߤ˼Ԥ㳰 Errno::EXXX ȯ
    

    ruby 1.7 feature: Ȥʸꤹȡɤ߹
    ǡ򤽤ʸ󥪥֥Ȥ˾񤭤֤ޤꤷʸ
    󥪥֥Ȥ餫 length ĹΰǤС;פʥ
    γƤԤޤ󡣻ꤷʸĹ length 
    ۤʤ硢ʸϰö length Ĺ˳ĥ(뤤Ͻ̾)
    ޤ(ơºݤɤ߹ǡΥˤʤޤ)

    ꤷ sysread θƤӽФǥǡǤä
    (sysread 㳰 EOFError ȯ)
    buf ϶ʸˤʤޤ

        buf = "x" * 20;
        io = File.open("/dev/null")
        p((io.sysread(10,buf) rescue nil))
        p buf
        => nil
           ""

