Hello World in Go

Hello World in Go

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Source code organization

Since GO1.11 we've had two ways of organizing go code: one is, using GOPATH and the second one is using go mod. GOPATH the structure was widely in use and kind of only way to structure your go code before GO1.11. In this blog, we'll use go mod since it provides more features and flexibility over GOPATH.

To know more about writing code with GOPATH read this blog.

Go programs are organized into packages, which enable code reusability. A package is a collection of source files in the same directory that are compiled together. Functions, types, variables, and constants defined in one source file are visible to all other source files within the same package.

The collection of packages that are bundled and released together is known as modules. These modules are stored in a repository. A repository may contain one or more modules but a Go repository typically contains only one module, located at the root of the repository.

It is recommended to use a remote repository path to organize Go code even though we're not going to publish it at the remote repository. For example, our hello world module name will be github.com/pratikjagrut/helloworld. A module can be defined locally without belonging to a repository. This module's path serves as an import prefix for its package. An import path is a string used to import a package.

Writing our first program

To start a new project, we'll first choose the module's pathname and then initialize it using go mod init. I'm choosing github.com/pratikjagrut/helloworld path, but you can choose a different one.

Create a project/module directory.

mkdir helloworld 
cd helloworld
go mod init github.com/pratikjagrut/helloworld
go: creating new go.mod: module github.com/pratikjagrut/helloworld

cat go.mod
module github.com/pratikjagrut/helloworld

go 1.16

While using repository pathname, make sure to change pratikjagrut to your username.

Now let's create a file main.go (any name will work followed by extension .go).

package main

import "fmt"

func main() {
  fmt.Println("Hello, world!")
}

In this code:

  • Declare the main package using the keyword package.

  • Import the popular fmt package using the keyword import.

  • Implement the main function to print a message to the console.

While developing the executable command, we use the main package. The main package tells the Go compiler that this package should compile as an executable program instead of a shared library.

Run the code.

go run .

Hello, world!

Run this code in Go Playground

As this is the main package, we can install the code as a command using go install.

go install is controlled by GOPATH and GOBIN environment variables. If the GOBIN environment variable is set, then the binary will install at the GOBIN location, else it will install at the $GOPATH/bin location. The default GOPATH ($HOME/go or %USERPROFILE%\go). To use the installed binary as a command, make sure the binary installation path is added to the $PATH variable.

go install .
helloworld

Hello, world!

We can make use of any command to install the bin.

go install
go install .
go install github.com/pratikjagrut/helloworld

Create and import packages from the same module

Here we'll create a utils package that will have only one function SwapStrings. SwapStrings starts with capital because we need to export it so that it could be used outside of the package utils.

mkdir utils # inside helloworld dir

Create a file utils.go in the utils dir with the following code.

package utils

func SwapStrings(a, b string) (string, string) {
  return b, a
}

We can build it to check if it compiles successfully.

go build

If it outputs nothing, then it means the compilation is successful. go build will also add this package to the local cache.

Now let's use this package in our executable program.

package main

import (
  "fmt"
  "github.com/pratikjagrut/helloworld/utils"
)

func main() {
  fmt.Println("Hello, world!")
  fmt.Println(utils.SwapStrings("Hello,", "world!"))
}
go run .

Hello, world!
world! Hello,

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