file - 从 Golang 中的文本文件中删除第一行

Question

我正在尝试弹出文件的第一行，从而逐行减少文件行。我删除第一行的实现如下

type FS struct {
    ...
    File       *os.File
}

//File creation ok...


func (fs *Fs) pop() []byte {
    var buf []string
    scanner := bufio.NewScanner(fs.File)
    //Reading lines
    for scanner.Scan() {
        line := scanner.Text()
        buf = append(buf, line)
    }
    //Writing from second line on the same file
    for s := 1; s < len(buf); s++ {
        fs.File.WriteString(fmt.Println(buf[s]))
    }
    //Commit changes
    fs.File.Sync()
    fs.File.Close()

    return []byte(buf[0])
}

我得到返回的 []byte 和预期的字符串，但文件永远不会改变。我在这里缺少什么？

Answer 1

pop the first line of a file and thus reduce the file lines one by one.

---

例如，

package main

import (
    "bytes"
    "fmt"
    "io"
    "os"
)

func popLine(f *os.File) ([]byte, error) {
    fi, err := f.Stat()
    if err != nil {
        return nil, err
    }
    buf := bytes.NewBuffer(make([]byte, 0, fi.Size()))

    _, err = f.Seek(0, io.SeekStart)
    if err != nil {
        return nil, err
    }
    _, err = io.Copy(buf, f)
    if err != nil {
        return nil, err
    }

    line, err := buf.ReadBytes('\n')
    if err != nil && err != io.EOF {
        return nil, err
    }

    _, err = f.Seek(0, io.SeekStart)
    if err != nil {
        return nil, err
    }
    nw, err := io.Copy(f, buf)
    if err != nil {
        return nil, err
    }
    err = f.Truncate(nw)
    if err != nil {
        return nil, err
    }
    err = f.Sync()
    if err != nil {
        return nil, err
    }

    _, err = f.Seek(0, io.SeekStart)
    if err != nil {
        return nil, err
    }
    return line, nil
}

func main() {
    fname := `popline.txt`
    f, err := os.OpenFile(fname, os.O_RDWR|os.O_CREATE, 0666)
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        return
    }
    defer f.Close()
    line, err := popLine(f)
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        return
    }
    fmt.Println("pop:", string(line))
}

$ cat popline.txtLorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.$ go run popline.gopop: Lorem ipsum dolor sit amet, consectetur adipiscing elit, $ cat popline.txtsed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.$