Your First Go Program

The classic Hello World program prints a single greeting. It is small enough to understand every line, and it tests the complete path from source file to running code.

Save the code below as main.go. Every executable Go program starts with package main and has a main function. The fmt package supplies convenient printing functions.

The program uses a function call: the name fmt.Println, followed by parentheses containing its argument. In this case the argument is a string literal.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

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() {
	fmt.Println("Hello, World!")
}

Output

Hello, World!

Go begins at main(), evaluates the string literal, calls fmt.Println, and writes the greeting plus a newline to standard output. The text is not stored permanently; it is displayed as the program runs.

• The file needs the .go extension.
• Use ordinary straight quotation marks in source code, not typographic “smart quotes”.

Make the program print Hello, Go! and then add a second fmt.Println call.

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

You have practiced Your First Go Program 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.