delete first N bytes from a text file

Question

Is there any function call or simple way to delete first N bytes from a text file in golang? Assuming that the file is contentiously appended by various go-routines, simultaneously I want to delete first N bytes of file.

Answer 1

You need to do f.Seek to jump over first bytes and than do regular reading, see example:

package main

import (
    "fmt"
    "io"
    "io/ioutil"
    "os"
)

func main() {
    f, err := os.Open(os.Args[1])            // open file from argument
    if err != nil {
        fmt.Println(err)
        return
    }

    var skipBytes int64 = 5                  // how many bytes to skip

    _, err = f.Seek(skipBytes, io.SeekStart) // skipping first bytes
    if err != nil {
        fmt.Println(err)
        return
    }

    buffer := make([]byte, 1024)               // allocating buffer to read
    for {
        n, err := f.Read(buffer)               // reading
        fmt.Print(string(buffer[:n]))          // writing to console
        if err != nil {
            fmt.Printf("Err: %v\n", err)
            return
        }
    }
}