In my talk i’ll guide you how to create user friendly, testable, and fancy command line applications.

1. Building robust and
friendly CLI apps

3. rclone
delve
cat
heroku
helm

4. Disclaimer:
No configs today

5. $ wc -l shakespeare.txt
124456 shakespeare.txt

6. os.Args - []string

9. Usage: docker [OPTIONS] COMMAND
A self-sufficient runtime for containers
Options:
--config string Location of client config files (default "/Users/andrii/.docker")
-D, --debug Enable debug mode
-H, --host list Daemon socket(s) to connect to
...
--tlsverify Use TLS and verify the remote
-v, --version Print version information and quit
Management Commands:
checkpoint Manage checkpoints
config Manage Docker configs
container Manage containers
image Manage images
network Manage networks
...
system Manage Docker
trust Manage trust on Docker images
volume Manage volumes
Commands:
attach Attach local standard input, output, and error streams to a running container
build Build an image from a Dockerfile
commit Create a new image from a container's changes
cp Copy files/folders between a container and the local filesystem
create Create a new container
deploy Deploy a new stack or update an existing stack
diff Inspect changes to files or directories on a container's filesystem
events Get real time events from the server
...
inspect Return low-level information on Docker objects
kill Kill one or more running containers

11. $ ls -la
User interface

12. Flags in linux/BSD
$ ls -ltrah

13. Long form flags:
$ ls
--color

14. Go flag system based on
Plan 9

15. $ ls -la
la

16. func main() {
var la = flag.String("la", "1 flag", "1 flag in golang.")
flag.Parse()
fmt.Println(*la)
}
➜ golang_for_two ./ls -la
flag needs an argument: -la
Usage of ./ls:
-la string
1 flag in golang. (default "1 flag")

17. GNU flags??

18. GNU flags??
GNU/UNIX-style
command-line arguments
- fork of flag pkg
- Docker has sub-package
- launchpad.net/gnuflag
- go-flags

19. GNU flags??launchpad.net/gnuflag
Supports:
✓ -l short flag
✓ -la for group of flags
✓ --color for long name
✓ Etc.

20. git add,
git commit
git push
$ app [global opts] cmd [cmd opts] args

21. Command-line
frameworks
✓ https://github.com/urfave/cli
(drone, cloudfoundry)
✓ https://github.com/spf13/cobra
(kubectl, hugo, rkt, docker,
helm, delve)

22. Part 2

24. ytop
Top 10 докладов
по кол-ву
просмотров и
лайков :)

25. ytop.sh v1

26. $ tree -L 3
.
!"" client_secret.json
!"" cmd
# $"" ytop
# !"" completion.go
# !"" list.go
# !"" root.go
# !"" root_test.go
# $"" ytop.go
!"" go.mod
!"" go.sum
!"" pkg
# !"" action
# # $"" list.go
4 directories, 11 files
Project layout

27. Task oriented
$ ytop list <playlist-id>

28. Task oriented in practise:
helm3 example of purge default flags
`helm delete --purge` is used
more often than not, so I suggest we
should make it the default convention for
Helm 3.
helm/helm/pull/5283
🔀

29. Task oriented:
helm3 example of purge default flags
helm/helm/pull/5283
🔀

30. Add tests:📝
func executeCommand(args ...string) (output string, err error)
{
buf := new(bytes.Buffer)
rootCmd := newRootCmd(buf, []string{})
rootCmd.SetOut(buf)
rootCmd.SetArgs(args)
_, err = rootCmd.ExecuteC()
return buf.String(), err
}
func TestListRootCommand(t *testing.T) {
output, err := executeCommand("list")
assert.NoError(t, err)
assert.Contains(t, output, "ytop list", output)
}

31. Actions pattern:
func newListCmd(out io.Writer) *cobra.Command {
cmd := &cobra.Command{
Use: "list",
Short: "list top youtube videos.",
Long: "list top youtube videos.",
Example: listExample,
RunE: func(cmd *cobra.Command, args []string) error {
return action.List()
},
}
return cmd
}

32. autocompletion:
func newCompletionCmd(out io.Writer) *cobra.Command {
var shells []string
for s := range completionShells {
shells = append(shells, s)
}
cmd := &cobra.Command{
Use: "completion SHELL",
Short: "Generate autocompletions script for the specified
shell (bash or zsh)",
Long: completionLong,
RunE: func(cmd *cobra.Command, args []string) error {
return runCompletion(out, cmd, args)
},
Args: cobra.ExactValidArgs(1),
ValidArgs: shells,
}
return cmd
}

33. autocompletion:
func runCompletionBash(w io.Writer, cmd *cobra.Command)
error {
err := cmd.Root().GenBashCompletion(w)
if err != nil {
return fmt.Errorf("error while generating bash
completion: %v", err)
}
return nil
}

34. Examples:
var listExample = `
List of youtube videos you would like to print:
$ youtube list <playlist-id>
`
func newListCmd(out io.Writer) *cobra.Command {
cmd := &cobra.Command{
Use: "list",
Short: "list top youtube videos.",
Long: "list top youtube videos.",
Example: listExample ,
}
return cmd
}

35. $ ./ytop list -h
list top youtube videos.
Usage:
ytop list [flags]
Examples:
# List of youtube videos you would like to
print:
$ youtube list <playlist-id>
Flags:
-h, --help help for list

36. Ship your CLI tool to
multiply OS:
🐳
https://raw.githubusercontent.com/YOU/YOURAPP/master/godownloader.sh
🏗

37. Aliases:

38. Aliases tl;dr:
type Command struct {
// Use is the one-line usage message.
Use string
// Aliases is an array of aliases that can be used instead of the first word in Use.
Aliases []string
$ ytop list --help
Usage:
ytop list [flags]
Aliases:
list, ls, l

39. Default to human output:
VIDEO ID LIKE COUNT TITLE
g8BD-0rIRN4 1232 Ricardo Jimenez - Quicksilver How Cloudflare …
op14_lAifQ4 597 Joan López de la Franca Beltran - From Chaos to …
KEUmOomnEqc 435 Roberto Clapis - Tackling Contention: The Monsters…
KUC5WtbBdFA 97 Johan Brandhorst - Writing REST Services for the ..

40. Friendly for both people
and scripts

41. Avoid sed/awk
$ ./ytop list <id>
| awk -F '|' '{print NR ". " $3}'
$ ./ytop list —output json
{“videoId”: 124, “likeCount”: 1000}

42. CLI Best Practices
https://bestpractices.coreinfrastructure.org/en/projects/3131#changecontrol

43. References:
📹 justforfunc #5: Defining a Color Flag in Go
📹 justforfunc #32: CLI tools with Cobra
📹 GopherCon 2019: Carolyn Van Slyck - Design
Command-Line Tools People Love
📖 The Go Programming Language by Alan A. A.
Donovan, Brian W. Kernighan
📖 Go in Practice by Matt Butcher, Matt Farina

45. Go на двоих
https://t.me/golang_for_two

46. Questions
? @a_soldatenkot.me/golang_for_two