Golang : How to remove certain lines from a file

Tags : golang remove-by-line file data-processing read-text-file

Alright, here is a simple tutorial on how to remove certain lines of data from a file. There are times due to some unforeseen reasons, some files that got downloaded contain more data that what was needed, such as extra HTTP request header information at the beginning of it.

So, how does one go around deleting those unwanted information?

The solution to this problem is similar to copying a file to a new file except that the unwanted data are omitted out during the copying process. For the code example below, we are going to remove the unwanted data at the beginning of the file simply be ignoring those lines. Once a marker %startHERE is detected, then only we start reading the rest of the data.

Here you go!

NOTE: For simplicity sake, we will use corruptFile constant to mimic a file. For your own production use, uncomment those lines to read from an actual file.

 package main

 import (

 const corruptFile = `HTTP 2.0 OK
 Content-Length :123456

 some real data bytes
 more bytes`

 func main() {

  // UNCOMMENT these lines to read in from an actual file instead.
  //if len(os.Args) <= 1 {
  // fmt.Printf("USAGE : %s <target_filename> \n", os.Args[0])
  // os.Exit(0)

  //fileName := os.Args[1]

  //fileBytes, err := ioutil.ReadFile(fileName)

  //if err != nil {
  // fmt.Println(err)
  // os.Exit(1)

  //lines := strings.Split(string(fileBytes), "\n")

  lines := strings.Split(string(corruptFile), "\n")

  startPrint := false

  for i, line := range lines {
 // only print after %startHERE
 if equal := strings.Index(line, "%startHERE"); equal > 0 {
 startPrint = true

 if startPrint {
 fmt.Println(i, line)
 // instead of printing to the screen, this is where
 // you want to start writing to a new file a.k.a copying the file

 // how it is done at https://www.socketloop.com/tutorials/golang-simple-file-scaning-and-remove-virus-example


Hope this helps and happy coding!

  See also : Golang : Display a text file line by line with line number example

Tags : golang remove-by-line file data-processing read-text-file

By Adam Ng(黃武俊)

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