Your first Go application

Programming in GO is quick and fun. You can write a working, compiled application with a few lines of code. In this example, we will use Visual Studio Code to edit the source code, and we have already configured it to start from the command line with the “code” command.

Write your first Go application

Create a directory for your application, let’s call it myapp

mkdir myapp

Open a terminal window in the myapp directory

cd myapp

Initialize the Go Modules. Go modules are available since Go version  1.11, in Go version 1.13 is the default over $GOPATH. In the main directory of your application execute

go mod init github.com/MY_USER_NAME/myapp

When we add an import statement to the code, Go will automatically update the go.mod file to include the dependency with the latest stable version. To list the referenced modules execute

go list -m all

Create a file for your module. This file is not required, but as it is on the top level, the package name is considered to be the name of the module.

code config.go

Enter to code

package myapp

func Config() string {
	return "Application config"
}

Create a sub-directory for the entry point of your application. When someone imports your application as a module this will be the command to execute.

mkdir -p cmd/myapp

Create the file for the command

code cmd/myapp/myapp.go

Create the main function

package main

import (
	"fmt"

	"github.com/MY_USER_NAME/myapp"
)

func main() {
	fmt.Println(myapp.Config())
}

Save the files and run the application

go run cmd/myapp/*

The output should be

Application config

Add a package to the application

mkdir mypackage

Create the package file

code mypackage/mypackage.go

Write the code of the package

package mypackage

func RunMyPackage() string {
	return "MyPackage running"
}

Update the main function to call the new package

code cmd/myapp/myapp.go

Add two lines to the code

package main

import (
	"fmt"

	"github.com/MY_USER_NAME/myapp"
	"github.com/MY_USER_NAME/myapp/mypackage" // NEW LINE
)

func main() {
	fmt.Println(myapp.Config())
	fmt.Println(mypackage.RunMyPackage()) // NEW LINE
}

Save the files and run the application. The output should be

go run cmd/myapp/*

Application config
MyPackage running

Using modules from other applications

To upgrade a module to the latest tagged version for example golang.org/x/text

go get golang.org/x/text

List all available versions of a module, for example, rsc.io/sampler

go list -m -versions rsc.io/sampler

Get a specific version of the module

go get rsc.io/sampler@v1.3.1

To remove unused dependencies from the go.mod and go.sum file

go mod tidy