gomod

In this lesson you’ll learn what a go.mod file is, how to create one, and how to manage dependencies with Go modules. A directory becomes a Go module when it contains a valid go.mod file in its root. Use go mod init to create this file and record the module path. Example: initialize a module

go mod init example.com/learn

A minimal go.mod looks like:

module example.com/learn

go 1.19

The file starts with a module declaration (module <module-path>).
It commonly includes the minimum supported Go version (here go 1.19).

Make sure the module path you choose is unique and, if you plan to publish the module, matches the repository location (for example github.com/<org>/<repo>). Changing the module path later can be disruptive.

Create main.go that imports a third-party package and uses it. Note the exported function name NewRandom() (capital R):

package main

import (
	"fmt"

	"github.com/pborman/uuid"
)

func main() {
	u := uuid.NewRandom()
	fmt.Println(u)
}

At this point the code imports a third-party package but you haven’t downloaded it yet. Use:

go mod tidy

What go mod tidy does

Adds missing module requirements needed to build the module.
Removes unused requirements.
Updates go.sum to match the resolved dependency graph. This keeps go.mod and go.sum in sync with your source code.

Representative output from go mod tidy:

go: finding module for package github.com/pborman/uuid
go: found github.com/pborman/uuid in github.com/pborman/uuid v1.2.1

After running go mod tidy, your go.mod will include resolved dependencies. Example:

module example.com/learn

go 1.19

require github.com/pborman/uuid v1.2.1

require github.com/google/uuid v1.0.0 // indirect

Run the program:

go run main.go

Example runtime output:

0fc766ac-80d1-4999-9ab4-701d50600cb8

Quick reference — common Go module commands

Command	Purpose	Example output / note
`go mod init <module-path>`	Create `go.mod` and set module path	`go mod init example.com/learn`
`go mod tidy`	Add missing deps and remove unused ones	Updates `go.mod` and `go.sum`
`go get <module>@<version>`	Add or upgrade a dependency	`go get github.com/pborman/uuid@v1.2.1`
`go mod download`	Download modules without building	Useful in CI

Links and references

Go Modules overview
github.com/pborman/uuid — package used in this example: https://github.com/pborman/uuid

Summary

A directory is a Go module when it contains a valid go.mod.
go.mod contains the module declaration, the minimum Go version, and required module dependencies.
Use go mod tidy frequently to keep go.mod and go.sum consistent with your code.
The replace directive can be used in go.mod to override module versions or point to local copies during development.

Use go mod tidy frequently during development to ensure go.mod and go.sum stay in sync with your source code.

Introduction

Introduction: Modules, Packages, and Imports

Core packages

API Development Project

CI/CD pipeline

Concurrency

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