"go get" command

"go get" command is the standard way of downloading and installing packages and related dependencies, and let's check the particulars of it through an example:
(1) Create a playstack repository in github;
(2) There is a LICENSE file and play directory in playstack folder;
(3) The play directory includes one main.go file:

package main

import (
    "fmt"
    "github.com/NanXiao/stack"
)

func main() {
    s := stack.New()
    s.Push(0)
    s.Push(1)
    s.Pop()
    fmt.Println(s)
}

The main package has one dependency package: stack. Actually, the main() function doesn't play anything meaningful, and we just use this project as a sample. So the directory structure of playstack looks like this:

.
├── LICENSE
└── play
    └── main.go

1 directory, 2 files

Clean the $GOPATH directory, and use "go get" command to download playstack:

# tree
.

0 directories, 0 files
# go get github.com/NanXiao/playstack
package github.com/NanXiao/playstack: no buildable Go source files in /root/gocode/src/github.com/NanXiao/playstack

"go get" command complains "no buildable Go source files in ...", and it is because the objects which "go get" works are packages, not repositories.There is no *.go source files in playstack, so it is not a valid package.

Tidy up $GOPATH folder, and execute "go get github.com/NanXiao/playstack/play" instead:

# tree
.

0 directories, 0 files
# go get github.com/NanXiao/playstack/play
# tree
.
├── bin
│   └── play
├── pkg
│   └── linux_amd64
│       └── github.com
│           └── NanXiao
│               └── stack.a
└── src
    └── github.com
        └── NanXiao
            ├── playstack
            │   ├── LICENSE
            │   └── play
            │       └── main.go
            └── stack
                ├── LICENSE
                ├── README.md
                ├── stack.go
                └── stack_test.go

11 directories, 8 files

We can see not only playstack and its dependency (stack) are all downloaded, but also the command (play) and library (stack) are all installed in the right place.

The mechanism behind "go get" command is it will fetch the repositories of packages and dependencies (E.g., use "git clone".), and you can check the detailed workflow by "go get -x":

# tree
.

0 directories, 0 files
# go get -x github.com/NanXiao/playstack/play
cd .
git clone https://github.com/NanXiao/playstack /root/gocode/src/github.com/NanXiao/playstack
cd /root/gocode/src/github.com/NanXiao/playstack
git submodule update --init --recursive
cd /root/gocode/src/github.com/NanXiao/playstack
git show-ref
cd /root/gocode/src/github.com/NanXiao/playstack
git submodule update --init --recursive
cd .
git clone https://github.com/NanXiao/stack /root/gocode/src/github.com/NanXiao/stack
cd /root/gocode/src/github.com/NanXiao/stack
git submodule update --init --recursive
cd /root/gocode/src/github.com/NanXiao/stack
git show-ref
cd /root/gocode/src/github.com/NanXiao/stack
git submodule update --init --recursive
WORK=/tmp/go-build054180753
mkdir -p $WORK/github.com/NanXiao/stack/_obj/
mkdir -p $WORK/github.com/NanXiao/
cd /root/gocode/src/github.com/NanXiao/stack
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/github.com/NanXiao/stack.a -trimpath $WORK -p github.com/NanXiao/stack -complete -buildid de4d90fa03d8091e075c1be9952d691376f8f044 -D _/root/gocode/src/github.com/NanXiao/stack -I $WORK -pack ./stack.go
mkdir -p /root/gocode/pkg/linux_amd64/github.com/NanXiao/
mv $WORK/github.com/NanXiao/stack.a /root/gocode/pkg/linux_amd64/github.com/NanXiao/stack.a
mkdir -p $WORK/github.com/NanXiao/playstack/play/_obj/
mkdir -p $WORK/github.com/NanXiao/playstack/play/_obj/exe/
cd /root/gocode/src/github.com/NanXiao/playstack/play
/usr/local/go/pkg/tool/linux_amd64/compile -o $WORK/github.com/NanXiao/playstack/play.a -trimpath $WORK -p main -complete -buildid e9a3c02979f7c6e57ce4452278c52e3e0e6a48e8 -D _/root/gocode/src/github.com/NanXiao/playstack/play -I $WORK -I /root/gocode/pkg/linux_amd64 -pack ./main.go
cd .
/usr/local/go/pkg/tool/linux_amd64/link -o $WORK/github.com/NanXiao/playstack/play/_obj/exe/a.out -L $WORK -L /root/gocode/pkg/linux_amd64 -extld=gcc -buildmode=exe -buildid=e9a3c02979f7c6e57ce4452278c52e3e0e6a48e8 $WORK/github.com/NanXiao/playstack/play.a
mkdir -p /root/gocode/bin/
mv $WORK/github.com/NanXiao/playstack/play/_obj/exe/a.out /root/gocode/bin/play

From the above output, we can see playstack repository is cloned first, then stack, At last the compilation and installation are executed.

If you only want to download the source files, and not compile and install, using "go get -d" command:

# tree
.

0 directories, 0 files
# go get -d github.com/NanXiao/playstack/play
# tree
.
└── src
    └── github.com
        └── NanXiao
            ├── playstack
            │   ├── LICENSE
            │   └── play
            │       └── main.go
            └── stack
                ├── LICENSE
                ├── README.md
                ├── stack.go
                └── stack_test.go

6 directories, 6 files

You can also use "go get -u" to update packages and their dependencies.

Reference:
Command go;
How does "go get" command know which files should be downloaded?.