“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: 

  1. package main
  3. import (
  4.     "fmt"
  5.     "github.com/NanXiao/stack"
  6. )
  8. func main() {
  9.     s := stack.New()
  10.     s.Push(0)
  11.     s.Push(1)
  12.     s.Pop()
  13.     fmt.Println(s)
  14. }

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: 

  1. .
  2. ├── LICENSE
  3. └── play
  4.     └── main.go
  6. 1 directory, 2 files

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

  1. # tree
  2. .
  4. 0 directories, 0 files
  5. # go get github.com/NanXiao/playstack
  6. 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: 

  1. # tree
  2. .
  4. 0 directories, 0 files
  5. # go get github.com/NanXiao/playstack/play
  6. # tree
  7. .
  8. ├── bin
  9. │   └── play
  10. ├── pkg
  11. │   └── linux_amd64
  12. │       └── github.com
  13. │           └── NanXiao
  14. │               └── stack.a
  15. └── src
  16.     └── github.com
  17.         └── NanXiao
  18.             ├── playstack
  19.             │   ├── LICENSE
  20.             │   └── play
  21.             │       └── main.go
  22.             └── stack
  23.                 ├── LICENSE
  24.                 ├── README.md
  25.                 ├── stack.go
  26.                 └── stack_test.go
  28. 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“: 

  1. # tree
  2. .
  4. 0 directories, 0 files
  5. # go get -x github.com/NanXiao/playstack/play
  6. cd .
  7. git clone https://github.com/NanXiao/playstack /root/gocode/src/github.com/NanXiao/playstack
  8. cd /root/gocode/src/github.com/NanXiao/playstack
  9. git submodule update --init --recursive
  10. cd /root/gocode/src/github.com/NanXiao/playstack
  11. git show-ref
  12. cd /root/gocode/src/github.com/NanXiao/playstack
  13. git submodule update --init --recursive
  14. cd .
  15. git clone https://github.com/NanXiao/stack /root/gocode/src/github.com/NanXiao/stack
  16. cd /root/gocode/src/github.com/NanXiao/stack
  17. git submodule update --init --recursive
  18. cd /root/gocode/src/github.com/NanXiao/stack
  19. git show-ref
  20. cd /root/gocode/src/github.com/NanXiao/stack
  21. git submodule update --init --recursive
  22. WORK=/tmp/go-build054180753
  23. mkdir -p $WORK/github.com/NanXiao/stack/_obj/
  24. mkdir -p $WORK/github.com/NanXiao/
  25. cd /root/gocode/src/github.com/NanXiao/stack
  26. /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
  27. mkdir -p /root/gocode/pkg/linux_amd64/github.com/NanXiao/
  28. mv $WORK/github.com/NanXiao/stack.a /root/gocode/pkg/linux_amd64/github.com/NanXiao/stack.a
  29. mkdir -p $WORK/github.com/NanXiao/playstack/play/_obj/
  30. mkdir -p $WORK/github.com/NanXiao/playstack/play/_obj/exe/
  31. cd /root/gocode/src/github.com/NanXiao/playstack/play
  32. /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
  33. cd .
  34. /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
  35. mkdir -p /root/gocode/bin/
  36. 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: 

  1. # tree
  2. .
  4. 0 directories, 0 files
  5. # go get -d github.com/NanXiao/playstack/play
  6. # tree
  7. .
  8. └── src
  9.     └── github.com
  10.         └── NanXiao
  11.             ├── playstack
  12.             │   ├── LICENSE
  13.             │   └── play
  14.             │       └── main.go
  15.             └── stack
  16.                 ├── LICENSE
  17.                 ├── README.md
  18.                 ├── stack.go
  19.                 └── stack_test.go
  21. 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?.