Overview

This command will basically match the go.mod file with the dependencies required in the source files.

• Download all the dependencies that are required in your source files and update go.mod file with that dependency.

• Remove all dependencies from the go.mod file which are not required in the source files.

Below is the usage format for the command

go mod tidy [-v]

With -v flag, go mod tidy will print information of all the unused modules removed from go.mod file if any

Example

Let’s see an an example. Create a module with import path as “learn“

go mod init learn

This command will create a go.mod file in the same directory. Since it is an empty module it doesn’t have any direct dependency specified yet. Let’s create a file named uuid.go in the same directory with the below contents

uuid.go

package main

import (
	"fmt"
	"strings"

	"github.com/pborman/uuid"
)

func main() {
	uuidWithHyphen := uuid.NewRandom()
	uuid := strings.Replace(uuidWithHyphen.String(), "-", "", -1)
	fmt.Println(uuid)
}

Notice that we have imported the dependency in the uuid.go as well

"github.com/pborman/uuid"

Let’s run the below command

go mod tidy

This command will download all the dependencies that are required in your source files and update go.mod file with that dependency. After running this command let’s now let’s again examine the contents of go.mod file

Do a cat go.mod

module learn

go 1.14

require github.com/pborman/uuid v1.2.1

It lists direct dependency which was specified in the uuid file along with exact version of the dependency as well. Now let’s check the go.sum file as well

Do a cat go.sum

github.com/google/uuid v1.0.0 h1:b4Gk+7WdP/d3HZH8EJsZpvV7EtDOgaZLtnaNGIu1adA=
github.com/google/uuid v1.0.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
github.com/pborman/uuid v1.2.1 h1:+ZZIw58t/ozdjRaXh/3awHfmWRbzYxJoAdNJxe/3pvw=
github.com/pborman/uuid v1.2.1/go.mod h1:X/NO0urCmaxf9VXbdlT7C2Yzkj2IKimNn4k+gtPdI/k=

Now let’s see one more example where go mod tidy will remove the dependency from go.mod file if it is not required in the source files. To illustrate this let’s remove the uuid.go file that we created above. Now run the command

go mod tidy -v

It will give below output

unused github.com/pborman/uuid

Now examine the contents of go.mod file. It will be as below

module learn

go 1.14

The

require github.com/pborman/uuid v1.2.1

line will be removed as it is not required in any of the source files. Also all entries of github.com/pborman/uuid and its depedencies will be removed from the go.sum file as well.