Building Awesome CLI apps in Go

BUILDING AN
AWESOME CLI
APP IN GO 1

ASHLEY MAC
•Dev Advocate at Rackspace
•Go newbie
•Slightly sarcastic
3

–Ashley Mac
“I have no idea what
i’m doing”
4

SPF13
•Willfully Unemployed
•Builds Cool Things With Go AKA
Gopher
•Irritatingly Specific
5

–Steve
“I Kinda Know What I'm
Doing”
6

MAKE SURE YOU
HAVE GO INSTALLED
AND WORKING +
AN EDITOR
7

HUMAN
INTERFACE
GUIDELINES
FOR CLIS 9

UNIx PHILOSOPHY
•Simple
•Clear
•Composable 
•Extensible
•Modular
•Small
12

– Rob Pike
“Many UNIX programs do quite
trivial things in isolation,
but, combined with other
programs, become general and
useful tools.”
13

– Doug McIlroy
“The manual page, which
really used to be a manual
page, is now a small volume,
with a thousand options”
14

› ls
› cp
› cat
› cd
list
copy
concatenate
change directory
ABBREVIATED
19

› ls
› cp
› cat
› cd
SHORT
20
Short
Clear
&

› ls
CONTExT
21
operates in current
Directory

› ls
HAS A LANGUAGE
23
List the contents 
of the directory I'm in

› ls
› rm
› zip
› find
COMMANDS
24
Verbs

› rm [file]
› cp [file] [newfile]
c:copy [file] [newfile]
INPUT
28

> rm [file] ... [fileN]
MANY INPUTS
29
Arg0 Argn

> cp [file] [newfile]
ORDER MATTERS
30
From To

SEPARATED
31
Space separates

DIRECT OBJECT
33
Verb Noun Noun

IS PROUNCABLE
34
Copy this file to here

› rm [options] [file]
c:del [options] [file]
MODIFY ACTIONS
37

› rm -f badfile.txt
SEPARATORS
38
Space separates

› rm --force
PREFIxED
39
prefix

-f == --force
SHORT VS LONG
42
Common Options
shortened

› rm -r -f rm -rf
STACKABLE
43
Short options stack

› rm --force [file]
ADVERB
45
Verb Adverb Noun

PRONOUNCEABLE
46
Forcefully remove 
this file

PRONOUNCEABLE
47
remove this file
with Force

› ls --color /home/spf13
FLAG INPUT
48
Verb Adverb Noun

› ls --color /home/spf13
PRONOUNCEABLE
49
Colorfully list my
home directory

› ls -a
MODIFY BEHAVIOR
51
List all the things

ADVERBS ExPRESS
•manner
•place
•time
•frequency
•degree
•level of
certainty
•etc.
53

ADVERBS ANSWER
•How?
•In what way?
•When?
•Where?
•To what
extent?
54

› ls -a
MODIFY BEHAVIOR
55
List completely
to what extent?

› ls --width=40
IMPUTABLE
56
Input
to what extent?

› ls --width 40
IMPUTABLE
57
Input
to what extent?

› ls --width 40
PREPOSITION
58
Verb Preposition Obj

› ls --width 40
PRONOUNCEABLE
59
list the directory with
a width of 40 cols

PREP PHRASE = ADVERB
•consists of a preposition and its
object
•acts as an adverb
•"Speaking at OSCON"
60

› tar -xcvf
FLAG = ACTION
63

› tar
First option must be a mode
specifier:
-c Create -r Add/Replace  
-t List -u Update -x Extract
FLAG = ACTION
64

Extract: tar -x [options]
-k Keep existing files
-m Don't restore mod times
FLAGS HAVING SUB FLAGS
67

Create: tar -c [options]
-z, -j, -J, --lzma
Compress archive with gzip/
bzip2/xz/lzma
FLAGS HAVING SUB FLAGS
68

ls [options]
-S sort by file size
-t sort by modification time
-U do not sort
...
INCOMPATIBLE FLAGS
70

ls -StU
INCOMPATIBLE FLAGS
71
What should this do?

> ls
--sort=[size,modtime,none]
BETTER
72

› git pull --stat --no-stat
FLAG --NO-FLAG
74

› git pull --stat
› git pull --stat=false
BETTER
75

› httpd
› vi
› emacs
› git
CLI APPS
77
Noun

APPS
•Launch something
•Do more than one thing
•Collection of commands
78

› svn add
› brew install
› npm search
› apt-get upgrade
› git clone
SUB COMMANDS
80

SUB COMMANDS
•CLI apps do multiple things
•Apps are groups of commands
•(sub) Commands have flags & args
•All rules still apply
81

› brew fetch -v hugo
ExPANDED RESOURCES
82
Cmd ArgApp Flag

› brew install hugo
NOUN
83
Verb ObjectNoun

› brew install hugo
PRONOUNCABLE
84
Brew, install hugo

PRONOUNCABLE
85
Verb Object
Noun adVerb

PRONOUNCABLE
86
Brew, verbosely  
fetch hugo

GOPATH AND SETUP
•You WILL store your code in a GitHub
user folder (example: $GOPATH/src/
github.com/username/helloworld)
•This was a pain in the ass
•I was comfortable with /code /dev/
or /projects 89

GOPATH AND SETUP
•By Storing code on github, I was
able to share my many problems
•Going from “I’m working on this”
to “let’s collaborate”
90

GOPATH
•The Go toolset uses an environment variable
called GOPATH to find Go source code.
•You can set GOPATH to anything you want,
but things will be easier if it’s set in your
home directory.
91

Windows:
c: setx GOPATH %USERPROFILE%
 
OS X:
❯ echo 'export GOPATH=$HOMEn' >> ~/.bash_profile
Close the terminal, reopen it, and type the following:
❯ echo $GOPATH
GO PATH
92

GOPATH AND SETUP
•Typing go get github.com/user/
project will download and build a
project.
93

EDITORS
•No IDE needed - any text editor will do.
•helpful features like autocomplete and
format & import on-save
•If you’re not sure what to use, I
recommend Atom — It’s free, cross-
platform, and easy to install. 94

PLUGINS
•Atom: https://github.com/joefitzgerald/go-plus
•Vim: https://github.com/fatih/vim-go
•included in http://vim.spf13.com/
•IntelliJ:  
https://plugins.jetbrains.com/plugin/?id=5047
•Full list:  
https://github.com/golang/go/wiki/
IDEsAndTextEditorPlugins 95

YOU DON’T NEED A
FRAMEWORK!
•The standard library has tons!
•Web server
•Templates
•Database
•etc.. 96

YOU DON’T NEED A
FRAMEWORK!
•Many Packages work
well together
•Very modular &
Composable 97

STANDARD LIBRARY
Let’s be honest, you don’t want to write everything from scratch so
most programming depends on your ability to interface with existing
libraries. i.e. packages. Here are a few core packages you should
know about;
•Strings
•Input/Output (io/ioutil)
•Errors
•fmt
98
• Containers and Sort
• path/filepath
• HTTP (net/http)
• math/rand

POWERFUL
CONCURRENCY 
BAKED IN
104

108
•Ken Thompson (B,C, Unix, UTF-8)
•Rob Pike (Unix, UTF-8)
•Robert Griesmier (Hotspot, JVM, V8)

MAJOR INFLUENCES
•C & derivatives
•Pascal & derivatives
•CSP
109

IDEALS
•Expressibility
•Edibility
•Powerful
•Simple
•Scalable
110

SPEC
•Java Spec : 670 pages
•YAML Spec : 84 pages
•Go Spec : 82 pages
111

KEYWORDS
•break
•default
•func
•interface
•select
•case
•defer
•go 112
•map
•struct
•chan
•else
•goto
•package
•switch
•const
•fallthrough
•if
•range
•type
•continue
•for
•import
•return
•var

BRACES
Compile Eror
114
Compile Error
/tmp/sandbox826898458/main.go:6: syntax error: unexpected
semicolon or newline before {

VARIABLES
117
Error
/tmp/sandbox473116179/main.go:6: one declared and not used /tmp/
sandbox473116179/main.go:7: two declared and not used /tmp/
sandbox473116179/main.go:8: three declared and not used

CLASSES  
( * SHOCKED
EXPRESSION *)119

NUMBERS
•Integers  
(numbers without a decimal)
•Floating-Point Numbers  
(numbers that contain a decimal)
• int, int8-64, uint, uint8-64, float32,64
124

STRINGS
•A string is a sequence of
characters
•Go strings are immutable
•Go strings are made up of
individual bytes (Usually one for each character)
125

type person struct { 
name string 
age int 
}
STRUCT
127

ARRAY
•An array is an ordered sequence
of elements of a single type
•Fixed length
•Arrays are indexed starting from 0
128

SLICE
•Segment of an array
•Dynamic length
•Can be used without thinking
about array underneath
129

MAP
•Unordered collection of key-value
pairs
•Similar to associative arrays, hash
tables, and dictionaries
•Dynamic Length 130

FUNCTION
•Function is a type
•First class citizen in Go
•Can have multiple input values
•Can have multiple return values
132

POINTERS
•Reference a location in memory
where a value is stored
•Represented using '*'
•Memory location referenced using '&'
133

DEFINE YOUR OWN TYPES
•Composed of other types
•Not aliases
134

METHOD
•Function defined on a type
135

GO HELP
The Go toolset has many different commands and
subcommands. You can pull up a list by typing:
go help
You now have everything you need to get started
137

GO FMT
•Formats your go code for you
•Awesome to do "on save"
•End of all stylistic debates
138

GO TEST
Writing code isn’t easy and humans make
mistakes so testing is really important, luckily, Go
includes a program that makes writing tests easier:
go test
Fun Fact: The Go compiler knows to ignore code
in files ending with _test.go
139

COMPILATION IS
VERY FAST
(USUALLY A
SECOND OR TWO)143

RESOURCES
•Getting Started, official golang page — https://golang.org/doc/
•Parse’s move from Ruby to Golang — http://blog.parse.com/
learn/how-we-moved-our-api-from-ruby-to-go-and-saved-our-sanity/
•Tutorial — Creating a Wiki — https://golang.org/doc/articles/
wiki/ (this was the first big tutorial that got me to build something
useful, take this one slow to get a grasps on its concepts)
•Golang — Concurrency is not Parallelism (Rob Pike), this video I
found super informative about go’s concurency and got me excited
to keep coding in Golang — https://youtu.be/cN_DpYBzKso
145

HTTP://
WWW.SLIDESH
ARE.NET/SPF13
148

HTTPS://
GITHUB.COM
/SPF13/TRI 149

SHOCKING
AMOUNT OF
TODO APPS 152

FEATURES
•Add Todo
•List Todos
•Mark "done"
•Search/Filter
•Priorities
•Archive
•Edit
•Create Dates
•Due Dates
•Tags
•Projects
156

› tri add "Add Priorities"
ADD
159

› tri add Add Priorities
ADD
160

› tri add "Add Priorities"
ADD
161
Verb Object
Noun

› tri add  
"Add Multi Todo Support"  
"Consider usage behaviors"
ADD
162

› tri add -p1 "Add listing" 
 
 
ADD WITH PRIORITY
164

 
 
ADD WITH PRIORITY
165
Verb Object
Noun adVerb

 
 
PRONOUNCEABLE
166
Tri, add "Add listing"
Todo with a pri of 1

› tri add "Add listing P:1" 
 
 
ALTERNATE SYNTAx
167

CONSIDERATIONS
•What priority system to use?
•Numeric
•Alpha
•High, Middle, Low
•What's the default priority? 168

MY TODO
•High, Middle, Low
•H=1, L=3, M/_=2
•Default is 2
169

› tri ls 
 
 
LISTING
171

› tri list 
 
 
LISTING
172

› tri 
 
 
LISTING
173

› tri list
(1) Add Listing
Consider usage behaviors
Add Multi Todo Support
Add Priorities
LISTING OUTPUT
174

› tri list
(1) Add Listing
Add Priorities
Add Multi Todo Support
LISTING OUTPUT
175

› tri list
(H) Add Listing
Add Priorities
(L) Add Multi Todo Support
LISTING OUTPUT
176

› tri list
(H) Add Listing
Add Priorities
(L) Add Multi Todo Support
LISTING OUTPUT
177

› tri list
1. (H) Add Listing
2. Consider usage behaviors
3. Add Priorities
4. (L) Add Multi Todo Support
LISTING OUTPUT
178

› tri list done 
 
 
TOKENS
180

› tri list -p1 
 
 
FLAGS
181

› tri list -p1
› tri list --due June
› tri list --created 12/15
› tri list --done -p1
FILTER BY PROPERTY
182

› tri list -p2
3. Add Priorities
FILTER BY PRIORITY
183

› tri list "Add"
1. (H) Add Listing
3. Add Priorities
SEARCHING
184

› tri list "Add" "Pri"
3. Add Priorities
SEARCHING
185

› tri list
1. (H) Add Listing
3. Add Priorities
LISTING OUTPUT
187

› tri done 2 
 
 
COMPLETING
188

› tri edit 1 "Improve Listing"
 
 
EDITING
189

› tri edit 1 -p2
› tri edit 2 --due 05/13/15
› tri edit 3 --created
12/15
EDITING
190

› tri edit 1 -p2
› tri list -p2
› tri edit 3 --created 12/15
› tri list --created 12/15
CONSISTENCY
191

› tri edit 1 2 3 -p2
BATCH EDIT?
192

•A CLI Command Framework
•A tool to generate CLI apps & commands
•Powers Kubernetes, Dropbox, Git Lfs,
CoreOS, Docker, Delve ...
195

› go get -u
github.com/spf13/cobra/cobra 
GET & INSTALL COBRA
196

› cobra
Cobra is a Cli library for Go that empowers applications. This 
application is a tool to generate the needed files to quickly 
create a Cobra application.
Usage:
cobra [command]
Available Commands:
add Add a command to a Cobra Application
COBRA
197

› cobra init  
github.com/<handle>/tri
-a "<Your Name>"
COBRA INIT
199
Replace with your url, 
project name & Name

› cobra init ...
Your Cobra application is
ready at
/Users/spf13/gopath/src/
github.com/spf13/tri
COBRA
200

› cd $GOPATH/src/
github.com/<name>/tri
CD TO PROJECT
201
Replace with your url,
project name & Name

› tree
.
├── LICENSE
├── cmd
│ └── root.go
└── main.go
LOOK AT YOUR PROJECT
202

› go build
› ./tri
 
A longer description that spans multiple lines
and likely contains examples
and usage of using your application. For
example...
BUILD & RUN IT
203

YOU'VE JUST
CREATED YOUR
1ST GO APP
204

OPEN THE
PROJECT IN
AN EDITOR 207

HTTPS://SOURCEFORGE.NET/PROJECTS/
LITEIDE/FILES/X29/ 210

package cmd 
 
import ( 
"fmt" 
"os" 
 
"github.com/spf13/cobra" 
"github.com/spf13/viper" 
)
CMD/ROOT.GO
212

package cmd 
 
import ( 
"fmt" 
"os" 
 
"github.com/spf13/viper" 
)
CMD/ROOT.GO
213
Notice package
name
Matches Dir

// This represents the base command when called
without any subcommands 
var RootCmd = &cobra.Command{ 
Use: "tri", 
Short: "A brief description of your
application", 
Long: `A longer description that spans multiple
lines and likely ... application.`, 
}
CMD/ROOT.GO
214

// This represents the base command when called
without any subcommands 
Use: "tri", 
Short: "Tri is a todo application", 
Long: `Tri will help you get more done in less time. 
It's designed to be as simple as possible to help you
accomplish your goals.`,
}
CMD/ROOT.GO
215

Use: "tri", 
...
CMD/ROOT.GO
216
Package level variable
& Exported

MAIN MAIN MAIN
•Go programs are all about "main"
•main.go (convention)
•main package
•main()
218

package main 
 
import "github.com/<yours>/tri/cmd" 
 
func main() { 
cmd.Execute() 
}
MAIN.GO
219

package main 
 
 
func main() { 
cmd.Execute() 
}
MAIN.GO
220
Package
Name

package main 
 
 
func main() { 
cmd.Execute() 
}
MAIN.GO
221
Function
Name

func Execute() { 
if err := RootCmd.Execute(); err !=
nil { 
fmt.Println(err) 
os.Exit(-1) 
} 
}
CMD/ROOT.GO
222
Package level 
variable

>go run main.go
Tri will help you get more done in
less time.
It's designed to be as simple as
possible to help you accomplish
your goals.
RUN IT
223

3. CREATING
OUR ADD
COMMAND 224

> cd $GOPATH/src/
github.com/spf13/tri
CD TO PROJECT
226
Replace with your url,
project name & Name

> cobra add add
add created at $GOPATH/src/
github.com/spf13/tri/cmd/
add.go
COBRA ADD ADD
227

> go run main.go add
add called
RUN "ADD"
228
Bill wants me to replace go run with

go build

./tri

var addCmd = &cobra.Command{ 
Use: "add", 
Short: "A brief description of your command", 
Long: `A longer description that spans multiple
lines and likely...`, 
Run: func(cmd *cobra.Command, args []string) { 
// TODO: Work your own magic here 
fmt.Println("add called") 
}, 
}
CMD/ADD.GO
231

Use: "add", 
Short: "Add a new todo", 
Long: `Add will create a new todo item to the list`, 
// TODO: Work your own magic here 
fmt.Println("add called") 
}, 
}
CMD/ADD.GO
232

func addRun(cmd *cobra.Command,
args []string){
fmt.Println("add called")
}
CMD/ADD.GO
233

Use: "add", 
Short: "Add a new todo", 
Long: `Add will create a new todo
item to the list`, 
Run: addRun, 
}
CMD/ADD.GO
234

func addRun(cmd *cobra.Command,
args []string) { 
for _, x := range args { 
fmt.Println(x) 
} 
}
CMD/ADD.GO
235

FOR x, Y := RANGE
•Provides a way to iterate over an array,
slice, string, map, or channel.
•Like Foreach or Each in other languages
•x is index/key, y is value
•_ allows you to ignore naming variables
236

func init() { 
RootCmd.AddCommand(addCmd) 
}
CMD/ADD.GO
237

INIT()
•Special function
•Called after package variable declarations
•Called prior to main.main()
•Each package may have multiple init()
•init() order un-guaranteed
238

> go run main.go add
"one two" three
 
one two
three
RUNNING ADD
239

4. CREATING
OUR DATA
MODEL 240

package todo 
 
type Item struct { 
Text string 
} 
TODO/TODO.GO
243

NAMED TYPES
•Can be any known type (struct,
string, int, slice, a new type you’ve
declared, etc)
•Methods can be declared on it
•Not an alias - Explicit type 244

import ( 
"fmt" 
 
"github.com/<yourname>/tri/todo" 
)
CMD/ADD.GO
246
Replace with
yourS

func addRun(...) { 
items := []todo.Item{} 
items = append(items, todo.Item{Text:x}) 
} 
fmt.Println(items) 
}
CMD/ADD.GO
247

} 
}
CMD/ADD.GO
248

APPEND
•Append adds new values to a slice
•Append will grow a slice as
needed
249

} 
}
CMD/ADD.GO
250

} 
}
CMD/ADD.GO
251

>go run main.go add  
"one two" three
[{one two} {three}]
GO RUN
252

var items = []todo.Item{} 
for _,x := range args { 
} 
fmt.Printf("%#vn", items) 
}
CMD/ADD.GO
253

>go run main.go add  
"one two" three
[]todo.Item{todo.Item{Text:
"one two"},
todo.Item{Text:"three"}}
GO RUN
254

func SaveItems(filename string, 
items []Item) error { 
 
return nil 
}
TODO/TODO.GO
257

import ( 
"encoding/json" 
)
TODO/TODO.GO
259

func SaveItems(filename string, items []Item) error { 
b, err := json.Marshal(items) 
if err != nil { 
return err 
} 
fmt.Println(string(b)) 
 
return nil 
}
TODO/TODO.GO
260

if err != nil { 
return err 
} 
 
return nil 
}
TODO/TODO.GO
261

if err != nil { 
return err 
} 
 
return nil 
}
TODO/TODO.GO
262

ERROR HANDLING
•Errors are not exceptional, they
are just values
•No exceptions in Go
•Errors should be handled when
they occur 263

( DON’T) PANIC
•Only use when:
1. You want to shut down your program AND
2. You need a stack trace
•Packages should never call Panic (only applications)
•Do not use as pseudo-exception handling
•Only recover a panic if you know you can properly
recover from it 264

if err != nil { 
return err 
} 
 
return nil 
}
TODO/TODO.GO
265

func addRun(cmd *cobra.Command,  
args []string) { 
items = append(items, todo.Item{Text: x}) 
} 
todo.SaveItems("x", items) 
}
CMD/ADD.GO
266

>go run main.go add
"one two" three
[{"Text":"one two"},
{"Text":"three"}]
CHECK JSON CREATION
267

import ( 
"io/ioutil" 
"encoding/json" 
)
TODO/TODO.GO
269

... 
err = ioutil.WriteFile(filename, b, 0644) 
if err != nil { 
return err 
} 
 
return nil 
}
TODO/TODO.GO
270

func addRun(cmd *cobra.Command,  
args []string) { 
}
 
err := todo.SaveItems("/Users/spf13/.tridos.json", items);
if err != nil { 
fmt.Errorf("%v", err) 
} 
}
CMD/ADD.GO
271

› go run main.go add "one two" three
› cat ~/.tridos.json
[{"Text":"one two"},
{"Text":"three"}]
CHECK FILE CREATION
272

func ReadItems(filename
string) ([]Item, error) { 
 
return []Item{}, nil 
}
TODO/TODO.GO
274

func ReadItems(filename
string) ([]Item, error) { 
 
return []Item{}, nil 
}
TODO/TODO.GO
275

func ReadItems(filename string)
([]Item, error) { 
b, err := ioutil.ReadFile(filename) 
if err != nil { 
return []Item{}, err 
}
...
TODO/TODO.GO
276

func ReadItems(filename string)
([]Item, error) { 
b, err := ioutil.ReadFile(filename) 
if err != nil { 
}
...
TODO/TODO.GO
277

func ReadItems(filename string) ([]Item, error) {
... 
var items []Item 
if err := json.Unmarshal(b, &items); err != nil { 
} 
return items, nil
}
TODO/TODO.GO
278

... 
var items []Item 
} 
return items, nil
}
TODO/TODO.GO
279

... 
var items []Item 
} 
return items, nil
}
TODO/TODO.GO
280

... 
var items []Item 
} 
return items, nil
}
TODO/TODO.GO
281

... 
var items []Item 
} 
return items, nil
}
TODO/TODO.GO
282

› cobra add list
list created at $GOPATH/
src/github.com/spf13/tri/
cmd/list.go
ADD LIST COMMAND
284

items, err := todo.ReadItems("/Users/
spf13/.tridos.json")
 
if err != nil { 
log.Printf("%v", err) 
} 
},
CMD/LIST.GO
285

 
if err != nil { 
} 
},
CMD/LIST.GO
286

 
if err != nil { 
} 
},
CMD/LIST.GO
287

› go run main.go list
[{one two} {three}]
RUN LIST
288

func addRun(cmd *cobra.Command, args []string) { 
var items = []todo.Item{}
 
 
}
...
CMD/ADD.GO
289

items, err := todo.ReadItems("/Users/spf13/.tridos.json") 
if err != nil { 
}
}
...
CMD/ADD.GO
290

6. ADDING
ROOT  
(GLOBAL)
FLAGS 291

› go get github.com/
mitchellh/go-homedir
GO GET
293

package cmd 
 
import ( 
... 
"github.com/mitchellh/go-homedir" 
)
CMD/ROOT.GO
294

var dataFile string
CMD/ROOT.GO
295

func init() { 
// Here you will define your flags and configuration settings 
// Cobra supports Persistent Flags which if defined here will
be global for your application 
 
home, err := homedir.Dir() 
if err != nil { 
log.Println("Unable to detect home directory. Please set
data file using --datafile.") 
}
...
CMD/ROOT.GO
296

func init() {
... 
RootCmd.PersistentFlags().StringVar(&dataFile, 
"datafile", 
home+string(os.PathSeparator)+".tridos.json", 
"data file to store todos")
...
CMD/ROOT.GO
298

func init() {
...
 
"datafile", 
CMD/ROOT.GO
299

func init() {
...
 
"datafile", 
CMD/ROOT.GO
300

func init() {
...
 
"datafile", 
CMD/ROOT.GO
301

items, err := todo.ReadItems(dataFile)
... 
err := todo.SaveItems(dataFile, items)
CMD/ADD.GO
302

items, err := todo.ReadItems(dataFile)
CMD/LIST.GO
303

› go build
› ./tri
...
Flags:
--datafile string data file to store todos (default "/
Users/spf13/.tridos.json")
-h, --help help for tri
Use "tri [command] --help" for more information about a
command.
SEE THE FLAG
304

› go build
› ./tri add "Add priorities"  
--datafile $HOME/.next.json
› ./tri list --datafile $HOME/.next.json
[{Add priorities}]
USE THE FLAG
305

› go run main.go add
"add priorities"  
"order by priority"
ADD SOME TODOS
307

Text string 
Priority int 
}
TODO/TODO.GO
309

func (i *Item) SetPriority(pri int) { 
switch pri { 
case 1: 
i.Priority = 1 
case 3: 
i.Priority = 3 
default: 
i.Priority = 2 
} 
}
TODO/TODO.GO
311

func (i *Item) SetPriority(pri int) { 
switch pri { 
case 1: 
i.Priority = 1 
case 3: 
i.Priority = 3 
default: 
i.Priority = 2 
} 
}
TODO/TODO.GO
312

func (i *Item) SetPriority (pri int) { 
switch pri { 
case 1: 
i.Priority = 1 
case 3: 
i.Priority = 3 
default: 
i.Priority = 2 
} 
}
TODO/TODO.GO
313

var priority int
... 
func init() { 
 
addCmd.Flags().IntVarP(&priority,  
"priority", "p", 2, "Priority:1,2,3")
...
CMD/ADD.GO
315

var priority int
... 
func init() { 
 
addCmd.Flags().IntVarP(&priority,  
"priority", "p", 2, "Priority:1,2,3")
...
CMD/ADD.GO
316

› go build
› ./tri help add
Add will create a new todo item to the list
Usage:
tri add [flags]
Flags:
-p, --priority int Priority:1,2,3 (default 2)
HELP ADD
317

... 
item := todo.Item{Text: x} 
item.SetPriority(priority) 
items = append(items, item) 
} 
CMD/ADD.GO
319

... 
item := todo.Item{Text: x} 
item.SetPriority(priority) 
items = append(items, item) 
} 
CMD/ADD.GO
320

› ./tri add "format list" -p1
› ./tri list
[{add priorities 0} {order by
priority 0} {format list 1}]
ADD WITH PRIORITY
321

// listCmd respresents the list command 
var listCmd = &cobra.Command{ 
Use: "list", 
Short: "List the todos", 
Long: `Listing the todos`, 
Run: listRun, 
} 
 
func listRun(cmd *cobra.Command, args []string) {
...
}
CMD/LIST.GO
324

...
w := tabwriter.NewWriter(os.Stdout, 3, 0, 1, ' ', 0) 
for _, i := range items { 
fmt.Fprintln(w, strconv.Itoa(i.Priority)+"t"+i.Text+"t") 
} 
 
w.Flush()
}
CMD/LIST.GO
326

...
} 
 
w.Flush()
}
CMD/LIST.GO
327

...
} 
 
w.Flush()
}
CMD/LIST.GO
328

...
} 
 
w.Flush()
}
CMD/LIST.GO
329

...
} 
 
w.Flush()
}
CMD/LIST.GO
330

0 add priorities
0 order by priority
1 format list
LIST W/PRIORITY
331

PRETTIER
PRIORITY 
PRINTING 332

func (i *Item) PrettyP() string { 
if i.Priority == 1 { 
return "(1)" 
} 
if i.Priority == 3 { 
return "(3)" 
} 
 
return " " 
}
TODO/TODO.GO
333

...
fmt.Fprintln(w, i.PrettyP()+"t"+i.Text+"t") 
} 
 
w.Flush()
}
CMD/LIST.GO
334

add priorities
order by priority
(1) format list
LIST W/PRIORITY
335

Text string 
Priority int 
position int 
}
TODO/TODO.GO
337

Text string 
Priority int 
position int 
}
TODO/TODO.GO
338
Notice
Lowercase p

func (i *Item) Label() string { 
return strconv.Itoa(i.position) + "." 
}
TODO/TODO.GO
339

func ReadItems(filename string) ([]Item, error) { 
... 
 
for i, _ := range items { 
items[i].position = i + 1 
} 
 
return items, nil 
}
TODO/TODO.GO
340

1. add priorities
2. order by priority
3. (1) format list
LIST W/PRIORITY
341

// ByPri implements sort.Interface for []Item based on 
// the Priority & position field. 
type ByPri []Item 
 
func (s ByPri) Len() int { return len(s) } 
func (s ByPri) Swap(i, j int) { s[i], s[j] = s[j], s[i] } 
func (s ByPri) Less(i, j int) bool { 
if s[i].Priority == s[j].Priority { 
return s[i].position < s[j].position 
} 
return s[i].Priority < s[j].Priority 
}
TODO/TODO.GO
343

 
} 
}
TODO/TODO.GO
344

 
} 
}
TODO/TODO.GO
345

 
} 
}
TODO/TODO.GO
346

 
} 
}
TODO/TODO.GO
347

 
} 
}
TODO/TODO.GO
348

func listRun(cmd *cobra.Command, args []string) { 
... 
 
sort.Sort(todo.ByPri(items)) 
 
w := tabwriter.NewWriter(os.Stdout, 3, 0, 1, ' ', 0)
...
CMD/LIST.GO
349

3. (1) format list
1. add priorities
2. order by priority
LIST W/PRIORITY
350

› cobra add done
done created at $GOPATH/
src/github.com/spf13/tri/
cmd/done.go
COBRA ADD DONE
353

// doneCmd represents the done command 
var doneCmd = &cobra.Command{ 
Use: "done", 
Aliases: []string{"do"}, 
Short: "Mark Item as Done", 
Run: doneRun, 
}
CMD/DONE.GO
354

Text string 
Priority int 
position int 
Done bool 
}
TODO/TODO.GO
356

TRI DONE  
SET  
.DONE 357

func doneRun(cmd *cobra.Command, args []string) { 
items, err := todo.ReadItems(dataFile) 
i, err := strconv.Atoi(args[0]) 
 
if err != nil { 
log.Fatalln(args[0], "is not a valid labeln", err) 
}
...
CMD/DONE.GO
358
Break out still

func doneRun(cmd *cobra.Command, args []string) { 
...
if i > 0 && i < len(items) { 
items[i-1].Done = true 
fmt.Printf("%q %vn", items[i-1].Text, "marked done")
 
sort.Sort(todo.ByPri(items)) 
todo.SaveItems(dataFile, items) 
} else { 
log.Println(i, "doesn't match any items") 
} 
}
CMD/DONE.GO
359
Break out slide

› go run main.go done a
2016/05/14 22:22:03 a is not
a valid label
strconv.ParseInt: parsing
"a": invalid syntax
DONE WRONG
360

› go run main.go done 13
2016/05/14 22:44:06 13
doesn't match any items
DONE WRONG
361

› go run main.go done 1
DONE RIGHT
362

func (i *Item) PrettyDone() string { 
if i.Done { 
return "X" 
} 
return "" 
}
TODO/TODO.GO
364

fmt.Fprintln(w, i.Label()
+"t"+i.PrettyDone()
+"t"+i.PrettyP()
+"t"+i.Text+"t") 
CMD/LIST.GO
365

if s[i].Done == s[j].Done { 
} 
} 
return !s[i].Done 
}
TODO/TODO.GO
366

1. (1) format list
2. X order by priority
3. X add priorities
LIST
367

› go run main.go add "hide
done items"
ADD NEW TODO
369

fmt.Fprintln(w, i.Label()
+"t"+i.PrettyDone()
+"t"+i.PrettyP()
+"t"+i.Text+"t") 
CMD/LIST.GO
370

var ( 
doneOpt bool 
)
CMD/LIST.GO
371

func init() { 
RootCmd.AddCommand(listCmd) 
 
listCmd.Flags().BoolVar(&doneOpt,
"done", false, "Show 'Done' Todos ")
}
CMD/LIST.GO
372

...
if i.Done == doneOpt { 
fmt.Fprintln(w, i.Label()...) 
} 
}
CMD/LIST.GO
373

› go run main.go list --done
4. X add priorities
TRY --DONE
374

var ( 
doneOpt bool 
allOpt bool 
)
CMD/LIST.GO
376

func init() { 
...
listCmd.Flags().BoolVar(&allOpt,
"all", false, "Show all Todos")
}
CMD/LIST.GO
377

...
if allOpt || i.Done == doneOpt { 
fmt.Fprintln(w, i.Label()...) 
} 
}
CMD/LIST.GO
378

› go run main.go list --all --done
1. (1) format list
2. hide done items
4. X add priorities
TRY --ALL
379

›./tri list --datafile
$HOME/Dropbox/Sync/tridos.json
›./tri add "Add config/ENV support"
--datafile $HOME/Dropbox/Sync/tridos.json
USING DIFFERENT DATA FILE
381

•A configuration manager
•Registry for application settings
•Works well with Cobra
383

VIPER SUPPORTS
•YAML, TOML, JSON or HCL
•Etcd, Consul
•Config LiveReloading
•default < KeyVal < config < env < flag
•Aliases & Nested values 384

var cfgFile string
func init() { 
cobra.OnInitialize(initConfig)
... 
RootCmd.PersistentFlags().StringVar(&cfgFile,
"config", "", "config file (default is
$HOME/.tri.yaml)") 
...
CMD/ROOT.GO
385
Already There

// Read in config file and ENV variables if set. 
func initConfig() { 
viper.SetConfigName(".tri")  
viper.AddConfigPath("$HOME") 
viper.AutomaticEnv()  
 
// If a config file is found, read it in. 
if err := viper.ReadInConfig(); err == nil { 
fmt.Println("Using config file:", viper.ConfigFileUsed()) 
}
}
CMD/ROOT.GO
386
Already There

STRICT
SEPARATION OF
CONFIG FROM
CODE 388

CONFIG IS STUFF
THAT VARIES IN
DIFFERENT
ENVIRONMENTS 389

CODE IS STUFF
THAT STAYS THE
SAME
EVERYWHERE 390

THE 12 FACTOR
APP STORES
CONFIG IN ENV
VARS 391

items, err := todo.ReadItems(dataFile))
...
if err := todo.SaveItems(dataFile), items); err != nil {
CMD/ADD.GO
393

items, err := todo.ReadItems(viper.GetString("datafile"))
...
if err := todo.SaveItems(viper.GetString("datafile"), items);
err != nil {
CMD/ADD.GO
394

func doneRun(cmd *cobra.Command, args []string) {
...
...
 
todo.SaveItems(viper.GetString("datafile"), items)
CMD/DONE.GO
395

...
CMD/LIST.GO
396

›./tri list --datafile
$HOME/Dropbox/Sync/tridos.json
›./tri add "Add config/ENV support"
--datafile $HOME/Dropbox/Sync/tridos.json
USING DIFFERENT DATA FILE
398

› DATAFILE=$HOME/Dropbox/Sync/trido.json
./tri list
› DATAFILE=$HOME/Dropbox/Sync/trido.json
./tri add "Add config/ENV support"
USING ENV
399

› export DATAFILE=$HOME/Dropbox/Sync/
trido.json
› ./tri list
1. Add config/ENV support
ExPORT FTW
400

// Read in config file and ENV variables if set. 
func initConfig() { 
viper.SetConfigName(".tri")  
viper.AddConfigPath("$HOME") 
viper.AutomaticEnv()
viper.SetEnvPrefix("tri") 
 
 
// If a config file is found, read it in. 
if err := viper.ReadInConfig(); err == nil { 
fmt.Println("Using config file:", viper.ConfigFileUsed()) 
}
CMD/ROOT.GO
402

› export TRI_DATAFILE=$HOME/Dropbox/
Sync/trido.json
› ./tri list
ExPORT FTW
403

› echo "datafile: /Users/
spf13/Dropbox/Sync/
trido.json" >
$HOME/.tri.yaml
CREATE CONFIG FILE
406

Using config file: /Users/
spf13/.tri.yaml
USE CONFIG FILE
407

TRY TO
IMPLEMENT
ExTRA FEATURES
409

FOLLOW US ON
TWITTER
@ASHLEYMCNAMARA
@SPF13
412

ADDITIONAL RESOURCES
•Ashley's Learn to Code Resources
•Steve's Blog
•Go Girls Who Code
413

Building Awesome CLI apps in Go

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