從Golang的文本文件中刪除第一行

Question

我試圖彈出文件的第一行，從而逐一減少文件行。 我去除第一線實現如下

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]) 
} 

我得到預期的字符串，但永遠不會改變的文件返回[]字節。 我在這裏錯過了什麼？

Answer 1

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, os.SEEK_SET) 
    if err != nil { 
     return nil, err 
    } 
    _, err = io.Copy(buf, f) 
    if err != nil { 
     return nil, err 
    } 
    line, err := buf.ReadString('\n') 
    if err != nil && err != io.EOF { 
     return nil, err 
    } 

    _, err = f.Seek(0, os.SEEK_SET) 
    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, os.SEEK_SET) 
    if err != nil { 
     return nil, err 
    } 
    return []byte(line), nil 
} 

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

 
$ cat popline.txt 
Lorem 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.go 
pop: Lorem ipsum dolor sit amet, consectetur adipiscing elit, 

$ cat popline.txt 
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. 

$