04 - Simple note app in Go

In this minimalist note program, we are going to:

• Create a CLI app that takes one argument, the name of the note
• Capture (read) user input and write the output into the note
• Deal with File, create, write and close

Start by create a new file simple-note/main.go

The command line argument

In Go, to capture the argument from the command line, we need to use os.Args

package main
import (
"fmt"
"os"
)

// Global Variables, we would also use a global "slice"
var (
	WorkDir  = "/tmp"
	FileName string
)

func checkArguments() {
	arguments := os.Args
	if len(arguments) == 2 {
		FileName = arguments[1] + ".txt" // we add .txt as file extension
	} else {
		fmt.Printf("Usage: %s <filename>\n", arguments[0])
		os.Exit(0)
	}
}

func main() {
checkArguments()
f := WorkDir + "/" + FileName
fmt.Println("Note will be written at ->", f)
}

You can try this with: go run main.go and go run main.go hello

Capture the user input

We capture the user input with bufio and os.Stdin. bufio.NewReader(os.Stdin) return a new Reader with a default buffer size of 4096 bytes.

import (
...
"bufio"
)

// this function would return a string
func captureMsg() string {
	fmt.Println("Please, enter your note")
	// User input for file content
	inputNote := bufio.NewReader(os.Stdin)
	// Read input and close buffer on '\n' (aka Enter)
	input, _ := inputNote.ReadString('\n')
	return input
}

func main() {
...
note := captureMsg()
fmt.Println("You have written", note)
}

And last, we need to save the “note” in a file.

Deal with files

To use files, we going to create two function createFile and writeInFile. We mainly use os.Create()

func createFile(filename, text string) {
	file, err := os.Create(filename)
	if err != nil {
		fmt.Println("Err creating a file", err)
		os.Exit(-1)
	}
	// closing running after the main method has completed
	defer func() {
		if err := file.Close(); err != nil {
			fmt.Println("Error closing file", err)
			os.Exit(-1)
		}
	}() // defer in anonymous function
	writeInFile(file, text)
}

// "file" should be a type os.File
func writeInFile(file *os.File, text string) {
	len, err := file.WriteString(text)
	if err != nil {
		fmt.Println("Failed writing to file", err)
		os.Exit(-1)
	}
	fmt.Printf("\nFile name is: %s", file.Name())
	fmt.Printf("\nNote length is: %d bytes\n", len)
}

Final program

package main

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

// Global Variables
var (
	WorkDir  = "/tmp"
	FileName string
)

func checkArguments() {
	arguments := os.Args
	if len(arguments) == 2 {
		FileName = arguments[1] + ".txt"
	} else {
		fmt.Printf("Usage: %s <filename>\n", arguments[0])
		os.Exit(0)
	}
}

func createFile(filename, text string) {
	file, err := os.Create(filename)
	if err != nil {
		fmt.Println("Err creating a file", err)
		os.Exit(-1)
	}
	// closing running after the main method has completed
	defer func() {
		if err := file.Close(); err != nil {
			fmt.Println("Error closing file", err)
			os.Exit(-1)
		}
	}() // defer in anonymous function
	writeInFile(file, text)
}

// "file" should be a type os.File
func writeInFile(file *os.File, text string) {
	len, err := file.WriteString(text)
	if err != nil {
		fmt.Println("Failed writing to file", err)
		os.Exit(-1)
	}
	fmt.Printf("\nFile name is: %s", file.Name())
	fmt.Printf("\nNote length is: %d bytes\n", len)
}

func captureMsg() string {
	fmt.Println("Please, enter your note")
	// User input for file content
	inputNote := bufio.NewReader(os.Stdin)
	// Read input and close buffer on '\n' (aka Enter)
	input, _ := inputNote.ReadString('\n')
	return input
}

func main() {
	checkArguments()
	f := WorkDir + "/" + FileName
	note := captureMsg()
	createFile(f, note)
}

This program is very minimalist, we would to improve it by adding:

• Improve the CLI by using more arguments and make “more things”
• List all notes from “WorkDir”
• Organise note by date or whatever
• Search a note by using keywords
• Delete a note, it will become a “tasklist” program :)