Overview

Below command can be used to download the dependency that is present in the go.mod file

go mod download

This command is used to pre download all the dependency before the application is run. go build as well as go install also will download the dependencies and also build the binary. go run will also download and and run the binary as well. go mod download command is used when you want to pre download the dependencies without build or running it.

Example

Let’s create a module first.

go mod init learn

Also let’s add direct dependency to the go.mod file too.

require github.com/pborman/uuid v1.2.1

With this dependency go.mod file will look like below.

module learn

go 1.14

require github.com/pborman/uuid v1.2.1

Now we need to download the newly added dependency. Fo that we can use the below command

go mod download

The command will download the github.com/pborman/uuid module as well all its dependencies. Also it will update the go.sum file with the checksum and version of all direct and indirect dependencies. 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=

go.sum file lists down the checksum of direct and indirect dependency required by the module.  github.com/google/uuid is internally used by the github.com/pborman/uuid . It is an indirect dependency of the module and hence it is recorded in the go.sum file.