In the days of yore, all programs were written from scratch—every utility function and every library to run the code had to written by hand. Now a days, we don't want to deal with the low level details on a regular basis; it would be unimaginable to write all the required libraries and utilities from scratch. Go comes with a rich library, which will be enough for most of our needs. However, it is possible that we might need a few extra libraries or features not provided by the standard library. Such libraries should be available on the internet, and we can download and add them into our project to start using them.

In the previous section, GOPATH, we discussed how all our projects are saved into qualified paths of the $GOPATH/src/git-server.com/user-name/my-go-project form. This is true for any and all dependencies we might have. There are multiple ways to handle dependencies in Go. Let's look at some of them.

The go get is the utility provided by the standard library for package management. We can install a new package/library by running the following command:

$ go get git-server.com/user-name/library-we-need

This will download and build the source code and then install it as a binary executable (if it can be used as a standalone executable). The go get utility also installs all the dependencies required by the dependency retrieved for our project.

The glide is one of the most widely used package management tool in Go community. It addresses the limitations of go get, but it needs to be installed manually by the developer. The following is a simple way to install and use glide:

$ curl https://glide.sh/get | sh
$ mkdir new-project && cd new-project
$ glide create
$ glide get github.com/last-ent/skelgor # A helper project to generate project skeleton.
$ glide install # In case any dependencies or configuration were manually added.
$ glide up # Update dependencies to latest versions of the package.
$ tree
.
├── glide.lock
├── glide.yaml
└── vendor
    └── github.com
        └── last-ent
            └── skelgor
                ├── LICENSE
                ├── main.go
                └── README.md  

In case you do not wish to install glide via curl and sh, other options are available and described in better detail on the project page, available at https://github.com/masterminds/glide.

The go dep is a new dependency management tool being developed by the Go community. Right now, it requires Go 1.7 or newer to compile, and it is ready for production use. However, it is still undergoing changes and hasn't yet been merged into Go's standard library.