Running Go Programs

Use go run when you want to compile and execute a program during development. Go builds a temporary executable and runs it for you.

In a directory containing a go.mod file and main.go, go run . runs the package in the current directory. For a simple standalone file, go run main.go also works. The dot means the current package, not the file literally named ..

A directory can contain several Go files belonging to the same package. Running the package includes those files; running one explicitly named file includes only the named source files.

Commands to try

go mod init example.com/steps
go run main.go
go run .

Initialize the module once, after opening your project directory. Do not reinitialize it on every run.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

func main() {
	for step := 1; step <= 3; step++ {
		fmt.Println("Step", step)
	}
}

Output

Step 1
Step 2
Step 3

The runner compiles the current program and executes main(). The loop prints three lines, then the process finishes. Changing the source and running the command again creates a fresh execution.

• go run is not a persistent web server or file watcher; it starts the program anew each time.
• go run main.go does not automatically include sibling Go source files.

Run the example once with go run main.go and once with go run . from a module directory. Compare results.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Running Go Programs in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.