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Video:

Application Entrypoint

August 22, 2021

Course Instructor: Elliot Forbes

Hey Gophers! My name is Elliot and I'm the creator of TutorialEdge and I've been working with Go systems for roughly 5 years now.

In the last video, we looked at setting up our Go project and getting all of the admin out of the way. However, the purpose of this course is to teach Go, so in this video, we’ll actually be doing a little bit of programming and creating the entrypoint for our application.

Our Application Entrypoint

Let’s create a new main.go file. Now this file is going to live under a cmd/cli/ directory. The reason for this is that, when building larger Go projects, you may want to expose your application as a REST API, or as a CLI or as a client app. For each of these examples, we want the entrypoint of our application to live within a dedicated directory under the cmd/ directory.

It’s important to note that whilst each of these directories will have it’s own main.go file, these files must only perform the action of startup and teardown of our application.

For example, if we were running a web server, we would want this file to initialize all of the components of our application and spin up a webserver using these components and then handle the graceful shutdown of our application.

For our CLI, we only want it parsing the incoming command and acting as a kind of router to the internal logic which will be housed within a different package/different directory entirely.

Our Starting Code

Let’s add some code to this newly created file now. For now, we’ll just keep it as a nice and lightweight Go app which just prints out Network CLI:

cmd/cli/main.go
package main

import "fmt"

func main() {
    fmt.Println("Network CLI")
}

We can then try running this from the root of our project like so:

$ go run cmd/cli/main.go
Network CLI

Perfect, we now have a starting point from which we can build upon.

Building

In production environments, whether it be for a CLI, or a server, your application will be run as a standalone binary executable.

Let’s now take a look at how we can build this application as a binary executable:

$ go build -o cli cmd/cli/main.go
OUTPUT FROM BUILD

You should see a new cli executable appear in the root directory of your project. We can then attempt to run this like we would any binary executable:

Note - You may have to set the execution bit on this executable file. For *Nix systems you can do that by typing: chmod +x cli.

./cli
Network CLI

Note - If you are on Windows, you may have to set the -o flag to cli.exe and run ./cli.exe in order for this to work.

Awesome, we have been able to compile our application as a binary executable and run it locally!

Installing Locally

The go tool can also handle the installing of binaries onto your local machine’s path for you. We can run go install in order to compile our application’s binary and then move it to a specific path which our local machine should already be setup to search:

$ go install cmd/cli/main.go
OUTPUT FROM INSTALL

We should now be able to run our cli command from any directory on our machine. Test this now by going up 1 directory and running ./cli and it should output Network CLI.

Conclusion

Perfect, in this video, we’ve created our application’s entrypoint and looked at how we can run our application using the go run command. We then looked at how we can take this a step further and compile our application as a binary and how we can use the go install command to also do the step of installing our application to our local machine’s PATH.