What is golang

Go (also known as Golang or Go language) is an open-source programming language mostly used to develop tools, command line interfaces, and websites. It relies on simplicity, dependability, and efficiency at its foundation to overcome the faults of its ancestors. Go is not the latest trend in programming language theory, or a buzz-word. Trust me it is a strong language to solve real-world program or so I hope.

golang unicorn by clgtart sticker shop

A quick golang tutorial

Go features garbage collection, a package system, first-class functions, lexical scope, and immutable UTF-8-based strings. It is quick to compile and execute, and its concurrency architecture is simple to comprehend. Additionally, Go features a robust standard library and a large, welcoming community.

This post is an hands-on introduction to Go using annotated example program. Learn by doing is the fast way to learn or so I hope.

Hello World

here is basic hello world look like

package main

import "fmt"

func main() {
    fmt.Println("hello world")
}

In this example program, we will build a simple tool that extract URL from a csv file. We could do it with just regular expression alone, however this is not a post about super effective, but as a learning steps.

So basically we will do:

• check a file if it exists (you will need this shit a lot in your golang life)
• read that file line by line (also this !)
• and for each line, split it into array
• loop through array find if any string is an URL

Golang check if file exists

Golang os.Stat() is a built-in function used to get the file status for a given file or directory. We can use it check if a file exists or not.

func exists(name string) bool {
    if _, err := os.Stat(name); err != nil {
        if os.IsNotExist(err) {
            return false
        }
    }
    return true
}

Golang read file line by line

We do not want to read the entire file into memory because it is a poor practice; reading the file line by line is far more effective and memory efficient.

file, err := os.Open("/path/to/file.txt")
if err != nil {
    log.Fatal(err)
}
defer file.Close()

scanner := bufio.NewScanner(file)

for scanner.Scan() {
    fmt.Println(scanner.Text())
}

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

Let's step through this.

First we use os.Open to open the file, and defer to close it. defer is used to ensure that a function call is performed later in a program’s execution, usually for purposes of cleanup. In our case it will close our file, ensure no memory leak.

Then later we use bufio.NewScanner to read the file line by line, print each like to stdin for make sure it work. (my habit)

Iterate over array

Instead of printing each line of the file to stdin, our basic software will break the line into an array. Lines in csv are frequently separated by commas, so here we go.

for scanner.Scan() {
    line := scanner.Text()
    for _, s := range strings.Split(line, ",") {
        // doing with s
    }
}

String starts with

We wanted to locate a URL, therefore we assumed that any text that begins with "http" is a URL.

if strings.HasPrefix(s, "http") {
    // extract s
}

Source code

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strings"
)

var filepath = "/path/to/file.txt"

func exists(name string) bool {
	if _, err := os.Stat(name); err != nil {
		if os.IsNotExist(err) {
			return false
		}
	}
	return true
}

func main() {
	result := []string{}
	if !exists(filepath) {
		log.Fatal("file not found!")
	}
	file, err := os.Open(filepath)
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)

	for scanner.Scan() {
		line := scanner.Text()
		for _, s := range strings.Split(line, ",") {
			if strings.HasPrefix(s, "http") {
				// extract s
				result = append(result, s)
			}
		}
	}

	if err := scanner.Err(); err != nil {
		log.Fatal(err)
	}
	// here is our extracted URL
	fmt.Println(result)
}

Further Reading

If you’ve made it to the end, congratulations! Hopefully, you had a lot of fun along the way. If you’d like to see more, check out the official Go website. There, you can follow the instruction, play interactively, and read a lot. Aside from a tour, the documentation concise overview of the language.

The source code for the standard library is must read for any Go developer. I learn a lot if it. It showcases the best of readable and understandable Go, Go style, and Go idioms. It is thoroughly documented and Alternatively, you can view the source code by clicking on a function name in the documentation!

Also check out Go by Example is another excellent resource for learning Go.

Codeacademy provides a free Learn Go course, which is worth a look.

Others articles of me write about golang

If you like golang, here is some others articles of the same author (me) about golang topic. Check it out !

1. golang error handling
2. golang context best practices
3. Golang composition over Inheritance all you need to know