How to delete specified lines in golang file

In development, we often need to operate files, including deleting and modifying some line data in the file. This article will teach you how to delete specified lines in a file using Golang language.

1. Read the file

Before deleting the specified line, we need to read the file data into memory first. Use Golang's built-in os and bufio packages to read the file as follows:

file, err := os.Open("example.txt")
if err != nil {
   fmt.Println(err)
}
defer file.Close()

scanner := bufio.NewScanner(file)
for scanner.Scan() {
   fmt.Println(scanner.Text())
}

The above code will open a file named example.txt file and use Scanner to read it line by line and output it. Now that we have read all the lines in the file, we will show you how to delete specific lines.

2. Delete specified lines

golang provides a variety of methods to delete lines in files, such as using the strings package and using the bytes package , but these methods are not flexible enough and inefficient. Here, we will use ioutil and strings packages to delete specified lines.

First, we need to read all the lines into slice and use the removeLine function to delete the lines we need:

func removeLine(filename string, lineToRemove int) error {
   content, err := ioutil.ReadFile(filename)
   if err != nil {
      return err
   }

   lines := strings.Split(string(content), "\n")
   if len(lines) > 0 && lines[len(lines)-1] == "" {
      lines = lines[:len(lines)-1]
   }

   if len(lines) < lineToRemove {
      return fmt.Errorf("invalid line number")
   }

   lines = append(lines[:lineToRemove], lines[lineToRemove+1:]...)
   output := strings.Join(lines, "\n")
   return ioutil.WriteFile(filename, []byte(output), 0644)
}

The above function Two parameters are required:

• filename, the file name of the specified line to be deleted.
• lineToRemove, the line number to be deleted.

First, we use the ioutil package ReadFile method to read the file data, and use the strings package SplitMethod split it by rows and store it in a slice. Next, we use the append method to remove the rows to be deleted from slice, and use the stringspackageJoin method to join all rows of data Reassemble into a string. Finally, we use the ioutilPackageWriteFile method to write the modified data back to the file.

3.Example

The following is a complete example that deletes the third row of data from the file.

package main

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

func main() {
   err := removeLine("example.txt", 2)
   if err != nil {
      fmt.Println(err)
   } else {
      fmt.Println("Line removed successfully!")
   }
}

func removeLine(filename string, lineToRemove int) error {
   content, err := ioutil.ReadFile(filename)
   if err != nil {
      return err
   }

   lines := strings.Split(string(content), "\n")
   if len(lines) > 0 && lines[len(lines)-1] == "" {
      lines = lines[:len(lines)-1]
   }

   if len(lines) < lineToRemove {
      return fmt.Errorf("invalid line number")
   }

   lines = append(lines[:lineToRemove], lines[lineToRemove+1:]...)
   output := strings.Join(lines, "\n")
   return ioutil.WriteFile(filename, []byte(output), 0644)
}

We can store the above code in the main.go file and create a file named example.txt to test it.

Finally, we need to execute the following command in the terminal:

go run main.go

Then we will see the terminal output Line removed successfully!, which indicates that we have successfully removed The third row of data.

4. Summary

In this article, we introduced how to use Golang language to delete specified rows of data in a file. We use the built-in packages os, bufio, ioutil and strings to achieve this functionality. Using the above method, you can easily delete any line in the file and freely locate the line you want to delete.

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