How to append a File in golang?

Understanding the Basics of File Appending in Go

File manipulation is a fundamental operation in programming, and Go provides powerful tools to handle various file-related tasks. Appending data to an existing file involves opening the file in append mode and writing the desired content.

Let's dive into the steps involved:

Step 1: Importing the Required Packages

Before we start appending data to a file, we need to import the necessary packages. In this case, we'll be using the os and fmt packages.


    package main

    import (
        "fmt"
        "os"
    )

Step 2: Opening the File in Append Mode

To open a file in append mode, we utilize the os.OpenFile function. This function allows us to specify the file path, the desired mode (in this case, os.O_APPEND), and the file permissions.


    func main() {
        filePath := "example.txt"
        file, err := os.OpenFile(filePath, os.O_APPEND|os.O_WRONLY, 0644)
        if err != nil {
            fmt.Println("Error:", err)
            return
        }
        defer file.Close()
        
        // Your appending logic goes here
    }

Step 3: Appending Data to the File

With the file opened in append mode, we can now write data to it. In this example, we'll append the text "Hello, World!" to the file.


    func main() {
        // ... (previous code)
        
        data := "Hello, World!\n"
        _, err = file.WriteString(data)
        if err != nil {
            fmt.Println("Error:", err)
            return
        }
        
        fmt.Println("Data appended successfully!")
    }

Step 4: Running the Code

To run the code, save it in a .go file (e.g., append_file.go) and execute it using the go run command:


    go run append_file.go

Example: Appending User Input to a File

Let's explore a more practical scenario by creating a program that allows users to input text, which will then be appended to a file. Below we use the bufio package to capture user input and append it to the file.


package main

import (
    "fmt"
    "os"
    "bufio"
)

    func main() {
        filePath := "user_notes.txt"
        file, err := os.OpenFile(filePath, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0644)
        if err != nil {
            fmt.Println("Error:", err)
            return
        }
        defer file.Close()
        
        reader := bufio.NewReader(os.Stdin)
        fmt.Print("Enter your note: ")
        userNote, _ := reader.ReadString('\n')
        
        _, err = file.WriteString(userNote)
        if err != nil {
            fmt.Println("Error:", err)
            return
        }
        
        fmt.Println("Note appended successfully!")
    }