string - 从文件中获取倒数第二行

Question

我找到了一种方法如何读取文件中的最后一行，但是文件中的最后一行是空的，我需要读取倒数第二行，但我不知道该怎么做，请帮忙。

func ll(z string) string {

    f, err := os.Open(z)
    if err != nil {
        log.Fatal(err)
    }
    bf := bufio.NewReader(f)
    for {
        switch line, err := bf.ReadString('\n'); err {
        case nil:
        // valid line, echo it.  note that line contains trailing \n.
        fmt.Println(line)

        case io.EOF:
            if line > "" {
                // last line of file missing \n, but still valid
                    fmt.Println(line, "in func")
            }
            return  line
        default:
            log.Fatal(err)
        }
    }
}

Answer 1

每次迭代只保存当前行，这样当遇到最后一行时，可以返回prev_line:

func next_to_last(z string) string {
    f, err := os.Open(z)
    if err != nil {
        log.Fatal(err)
    }
    bf := bufio.NewReader(f)
    prev_line := ""

    for {
        switch line, err := bf.ReadString('\n'); err {

        case nil:
        // valid line, echo it.  note that line contains trailing \n.
        fmt.Println(line)
        prev_line = line // Save line as previous

        case io.EOF:
            if line > "" {
                // last line of file missing \n, but still valid
                    fmt.Println(line, "in func")
            }
            return  prev_line // Return previous line

        default:
            log.Fatal(err)
        }
    }
}