Switch by Using do{} Creatively

• Another interesting approach to a switch statement is arrange for a do block to return the proper value:

    $amode = do {
    if     ($f & O_RDONLY) { "r" }       # XXX: isn't this 0?
    elsif  ($f & O_WRONLY) { ($f & O_APPEND) ? "a" : "w" }
    elsif  ($f & O_RDWR)   {
      if ($f & O_CREAT)    { "w+" }
      else                 { ($f & O_APPEND) ? "a+" : "r+" }
    }
    };