--- exec(command)
--- exec(program[, arg1[, arg2[, ...]]])

    command ǻꤵ줿ޥɤ¹Ԥޤץμ¹ԥ
    ɤϤΥޥ(뤤 shell)ˤʤΤǡư
    硢δؿޤ󡣵ư˼Ԥruby 󥿥ץ꥿
    椬äϡ㳰 Errno::EXXX ȯޤ

    ܤηǤ command  shell Υ᥿ʸ
    (* ? {} [] <> () ~ & | \ $ ; ' ` " \n)ޤ硢
    shell ͳǼ¹ԤޤǤʤХ󥿥ץ꥿ľ
    ¹Ԥޤ

    ܤηǤϡ shell ͳ˼¹Ԥޤ
    ξˤ϶ shell Υ᥿饯⤽Τޤ
    program ΰϤޤ
    Ƭΰ2ǤǤä硢1Ǥʸ󤬼ºݤ
    ưץΥѥǤꡢ2Ǥ֤ߤפΥץ
    ̾ˤʤޤ
    ruby 1.8 feature: ΤȤ1ǤեѥǻꤷʤƤ
    Ķѿ PATH õޤ

