Working with the File System in Go: A Practical Guide

Working with the File System in Go: A Practical Guide

Go (Golang) is a modern compiled language that is excellent for building server applications, utilities, and command-line tools. One of the key tasks in such projects is working with the file system. In this article, we will cover practical examples: from opening and reading files to recursively traversing directories. All examples are written in pure Go without third-party libraries.

Basics: Opening, Reading, and Writing Files

The os package provides functions for low-level file operations. To read the entire contents of a file into memory, use os.ReadFile (available since Go 1.16).

package main

import (    "fmt"    "os")

func main() {    data, err := os.ReadFile("example.txt")    if err != nil {        fmt.Println("Error reading file:", err)        return    }    fmt.Println(string(data))}

To write data to a file, use the os.WriteFile function. It creates the file if it does not exist, or overwrites an existing one.

package main

import (    "fmt"    "os")

func main() {    content := []byte("Hello, Go!Second line")    err := os.WriteFile("output.txt", content, 0644)    if err != nil {        fmt.Println("Error writing:", err)        return    }    fmt.Println("File successfully written")}

The third argument 0644 is the Unix-style permission (owner can read and write, others can only read). On Windows, this parameter is partially ignored.

Streaming Read and Write: Working with Large Files

For working with large files (more than a few megabytes), you should not load them entirely into memory. Use buffered reading via bufio or the io package.

package main

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

func main() {    file, err := os.Open("large_file.log")    if err != nil {        fmt.Println("Error opening:", err)        return    }    defer file.Close()

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

    if err := scanner.Err(); err != nil {        fmt.Println("Scanning error:", err)    }}

For streaming writes, use bufio.NewWriter:

package main

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

func main() {    file, err := os.Create("output_stream.txt")    if err != nil {        fmt.Println("Error creating:", err)        return    }    defer file.Close()

    writer := bufio.NewWriter(file)    for i := 0; i < 10; i++ {        _, err := writer.WriteString(fmt.Sprintf("Line %d", i+1))        if err != nil {            fmt.Println("Error writing:", err)            return        }    }    writer.Flush() // Important: flush the buffer    fmt.Println("Writing completed")}

The Flush() method is mandatory — without it, data may remain in the buffer and not be written to the file.

Working with Directories: Creating, Deleting, and Traversing

You can create a new directory using os.Mkdir (single folder) or os.MkdirAll (recursively, like mkdir -p).

package main

import (    "fmt"    "os")

func main() {    // Create a single folder    err := os.Mkdir("new_folder", 0755)    if err != nil {        fmt.Println("Error creating folder:", err)    }

    // Create a nested structure    err = os.MkdirAll("a/b/c/d", 0755)    if err != nil {        fmt.Println("Error creating nested folders:", err)    } else {        fmt.Println("Folders created")    }}

Deleting a directory is done via os.Remove (only if empty) or os.RemoveAll (recursively).