Writing a CLI for Log Parsing in Go

Table of Contents

  1. Introduction
  2. Prerequisites
  3. Setting Up the Project
  4. Parsing Log Files
  5. Filtering Log Entries
  6. Exporting Results
  7. Conclusion

Introduction

In this tutorial, we will learn how to write a command-line interface (CLI) tool in Go for parsing log files. We will explore the basics of Go programming, file input/output operations, and filtering log entries based on specific criteria. By the end of this tutorial, you will have gained knowledge and practical experience in building a log parsing CLI tool using Go.

Prerequisites

To follow along with this tutorial, you should have a basic understanding of the Go programming language and have Go installed on your machine. If you are new to Go, it is recommended to go through the official Go tour (tour.golang.org) or the Getting Started guide on golang.org.

Setting Up the Project

Let’s begin by setting up our project:

  1. Create a new directory for your project, e.g., log-parser-cli.
  2. Navigate to the project directory: cd log-parser-cli.

  3. Initialize a new Go module: go mod init logparser.

  4. Create a new Go source file named main.go.

Parsing Log Files

In this section, we will implement the functionality to parse log files. We will read the log file line by line and process each line individually.

package main

import (
	"fmt"
	"log"
	"os"
)

func main() {
	filePath := os.Args[1] // Get log file path from command-line argument

	file, err := os.Open(filePath)
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	// Read the file line by line and process each line
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := scanner.Text()

		// Process the log entry
		// TODO: Implement log entry processing logic

		fmt.Println(line)
	}

	if err := scanner.Err(); err != nil {
		log.Fatal(err)
	}
}

Explanation:

  • We retrieve the log file path passed as a command-line argument using os.Args[1]. Make sure to handle the case when the argument is missing or incorrect.
  • We open the log file using os.Open() and handle any possible errors.
  • We use a bufio.Scanner to read the file line by line.
  • Inside the loop, we can process each line individually. Currently, we are printing each line using fmt.Println(). Replace this line with your own logic to process the log entry.

Filtering Log Entries

Now, let’s enhance our log parsing CLI tool by adding the ability to filter log entries based on certain criteria. For example, we can filter log entries based on a specific error level.

// ...

func main() {
	// ...

	filter := os.Args[2] // Get the filter criteria from the command-line argument
	// TODO: Validate and parse the filter criteria

	// ...

	for scanner.Scan() {
		line := scanner.Text()

		// Filter the log entry based on the criteria
		// TODO: Implement log entry filtering logic

		fmt.Println(line)
	}

	// ...
}

// ...

Explanation:

  • We retrieve the filter criteria from the command-line argument using os.Args[2]. Again, make sure to handle the case when the argument is missing or incorrect.
  • Replace the TODO comments with your own logic to validate and parse the filter criteria.
  • Inside the loop, before printing each line, apply the filter criteria to decide whether to include or exclude the log entry.

Exporting Results

In this section, we will add the functionality to export the parsed and filtered log entries to a file.

// ...

func main() {
	// ...

	outputFile := os.Args[3] // Get the output file path from the command-line argument

	output, err := os.Create(outputFile)
	if err != nil {
		log.Fatal(err)
	}
	defer output.Close()

	// ...

	for scanner.Scan() {
		line := scanner.Text()

		// ...

		output.WriteString(line + "\n")
	}

	// ...
}

// ...

Explanation:

  • We retrieve the output file path from the command-line argument using os.Args[3].
  • We create the output file using os.Create() and handle any possible errors.
  • Inside the loop, before printing each line, we write the line to the output file using output.WriteString(line + "\n").

Conclusion

In this tutorial, we have learned how to write a CLI tool in Go for parsing log files. We explored the basics of Go programming, file input/output operations, and filtering log entries based on specific criteria. You now have the knowledge and practical experience to build your own log parsing CLI tool using Go. Feel free to enhance the tool further by adding more features, such as timestamp filtering or log entry statistics.

Remember to always follow best practices, such as error handling and code organization, when developing Go applications. Go’s simplicity and performance make it an excellent choice for building command-line tools and other applications.

Published:

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