# Hello, World and the go Command — Go (Golang)

Source: https://www.skillbyai.com/en/go/i-hello

> go run, go build, go mod init.

## One tool for everything

The `go` command builds, runs, tests and manages dependencies: `go mod init example.com/app` creates a module, `go run .` compiles and runs the package in the current directory, `go build` produces a binary, `go test ./...` runs tests, `go vet` finds suspicious code and `gofmt` formats it. A program starts in `package main` at `func main()`. Imports must be used, and unused variables are compile errors, which keeps code clean.

## A first program, run

I ran this with Go 1.27.1 (`go run .` in a module named demo, standard library only). fmt.Printf formats with verbs such as %s for strings and %d for integers.

```go
package main

import "fmt"

func main() {
	name := "Gopher"
	fmt.Printf("Hello, %s! You have %d new messages.\n", name, 3)
}
```

Output:

```
Hello, Gopher! You have 3 new messages.
```

## Use go run while learning

go run . compiles and runs in one step; use go build when you need the binary.

**Quiz:** Where does a Go program start running?

- [x] func main() in package main
- [ ] The first function in any file
- [ ] init.go
- [ ] A class with a static main method

*Answer:* func main() in package main. package main + func main.