This document discusses building command line applications in Ruby. It covers using OptionParser and Mixlib::CLI for parsing arguments, Thor for building commands, testing CLI apps, interacting with the system via libraries like Mixlib::ShellOut, and logging to standard output and error. The target audience is developers looking to get started with Ruby command line programs.

1. Ruby on Rails In Practice
Apartment List and Thoughtbot
San Francisco, September 2012
Getting started with
Command Line Applications

2. Ruby on Rails In Practice
Apartment List and Thoughtbot
San Francisco, September 2012
Getting started with
Command Line Applications
Nikhil Mungel
@hyfather

3. Why CLI ?

4. CLI

5. Scriptable
CLI Lightweight
Consistent UX

6. Why Ruby?

8. • Textual Manipulation
• OO & FP Abstractions
• Plethora of CLI gems
• Examples to learn from

9. The Structure

11. Input Execution Output

12. Input Execution Output
STDIO = UI/UX

13. Input
STDIN

14. Input
ARGV/ENV
STDIN

15. Input
ARGV/ENV
STDIN

16. Input
ARGV/ENV
STDIN

17. Input
OptionParser
ARGV/ENV
STDIN

18. Input
OptionParser
ARGV/ENV
STDIN

19. Input Libraries
OptionParser
ARGV/ENV
STDIN

20. Input Libraries
OptionParser
ARGV/ENV
STDIN

21. Input Libraries
OptionParser
ARGV/ENV
STDIN

22. options = {}
OptionParser.new do |opts|
opts.banner = "Usage: example.rb [options]"
opts.on("-v", "--[no-]verbose", "Run verbosely") do |v|
options[:verbose] = v
end
end.parse!

23. options = {}
OptionParser.new do |opts|
opts.banner = "Usage: example.rb [options]"
opts.on("-v", "--[no-]verbose", "Run verbosely") do |v|
options[:verbose] = v
end
end.parse!
~ > ./opt.rb --help
Usage: example.rb [options]
-v, --[no-]verbose Run verbosely

24. options = {}
OptionParser.new do |opts|
opts.banner = "Usage: example.rb [options]"
opts.on("-v", "--[no-]verbose", "Run verbosely") do |v|
options[:verbose] = v
end
end.parse!
~ > ./opt.rb --help
Usage: example.rb [options]
-v, --[no-]verbose Run verbosely

25. options = {}
OptionParser.new do |opts|
opts.banner = "Usage: example.rb [options]"
opts.on("-v", "--[no-]verbose", "Run verbosely") do |v|
options[:verbose] = v
end
end.parse!
~ > ./opt.rb --help
Usage: example.rb [options]
-v, --[no-]verbose Run verbosely

26. options = {}
OptionParser.new do |opts|
opts.banner = "Usage: example.rb [options]"
opts.on("-v", "--[no-]verbose", "Run verbosely") do |v|
options[:verbose] = v
end
end.parse!
~ > ./opt.rb --help
Usage: example.rb [options]
-v, --[no-]verbose Run verbosely

27. The Mixlib Suite

28. class MyCLIApp
include Mixlib::CLI
option :config_file,
:short => "-c CONFIG",
:description => "Configuration file",
:required => true
end
~ > ./mycliapp.rb --help
Usage: ./mix.rb (options)
-c, --config CONFIG Configuration file (required)
-h, --help Show this message

29. class MyCLIApp
include Mixlib::CLI
option :config_file,
:short => "-c CONFIG",
:description => "Configuration file",
:required => true
end
~ > ./mycliapp.rb --help
Usage: ./mix.rb (options)
-c, --config CONFIG Configuration file (required)
-h, --help Show this message

30. class MyCLIApp
include Mixlib::CLI
option :config_file,
:short => "-c CONFIG",
:description => "Configuration file",
:required => true
end
~ > ./mycliapp.rb --help
Usage: ./mix.rb (options)
-c, --config CONFIG Configuration file (required)
-h, --help Show this message

31. config.rb
server_url “http://server.remote”
username “elvis”
password “hotdog”

32. config.rb
server_url “http://server.remote”
username “elvis”
password “hotdog”
class MyConfig
extend(Mixlib::Config)
server_url 'http://server.local'
username 'king'
password 'burger'
end
MyConfig.from_file(‘config.rb’)
irb> MyConfig.server_url
# ‘http://server.remote’

33. config.rb
server_url “http://server.remote”
username “elvis”
password “hotdog”
class MyConfig
extend(Mixlib::Config)
server_url 'http://server.local'
username 'king'
password 'burger'
end
MyConfig.from_file(‘config.rb’)
irb> MyConfig.server_url
# ‘http://server.remote’

34. Thor

35. class Test < Thor
desc " FILE", "an example task"
method_option :delete,
:aliases => "-d",
:desc => "Delete the file"
def example(file)
end
end

36. class Test < Thor
desc " FILE", "an example task"
method_option :delete,
:aliases => "-d",
:desc => "Delete the file"
def example(file)
end
end
~ > myapp help test:example
Usage:
thor test:example FILE
Options:
-d, [--delete=DELETE] # Delete the file after parsing it
an example task

37. class Test < Thor
desc " FILE", "an example task"
method_option :delete,
:aliases => "-d",
:desc => "Delete the file"
def example(file)
end
end
~ > myapp help test:example
Usage:
thor test:example FILE
Options:
-d, [--delete=DELETE] # Delete the file after parsing it
an example task

38. class Test < Thor
desc " FILE", "an example task"
method_option :delete,
:aliases => "-d",
:desc => "Delete the file"
def example(file)
end
end
~ > myapp help test:example
Usage:
thor test:example FILE
Options:
-d, [--delete=DELETE] # Delete the file after parsing it
an example task

39. class Test < Thor
desc " FILE", "an example task"
method_option :delete,
:aliases => "-d",
:desc => "Delete the file"
def example(file)
end
end
~ > myapp help test:example
Usage:
thor test:example FILE
Options:
-d, [--delete=DELETE] # Delete the file after parsing it
an example task

40. class Test < Thor
desc " FILE", "an example task"
method_option :delete,
:aliases => "-d",
:desc => "Delete the file"
def example(file)
end
end
~ > myapp help test:example
Usage:
thor test:example FILE
Options:
-d, [--delete=DELETE] # Delete the file after parsing it
an example task

41. class Test < Thor
desc " FILE", "an example task"
method_option :delete,
:aliases => "-d",
:desc => "Delete the file"
def example(file)
end
end
~ > myapp help test:example
Usage:
thor test:example FILE
Options:
-d, [--delete=DELETE] # Delete the file after parsing it
an example task

42. class Test < Thor
desc " FILE", "an example task"
method_option :delete,
:aliases => "-d",
:desc => "Delete the file"
def example(file)
end
end
~ > myapp help test:example
Usage:
thor test:example FILE
Options:
-d, [--delete=DELETE] # Delete the file after parsing it
an example task

43. Testing!

45. Input Execution Output

46. Input Execution Output

47. Input Execution Output
Mostly third party libraries

48. Input Execution Output
Test::Unit, rspec etc.

49. Input Execution Output
System

50. System

51. System
File System Network Process

52. Isolated
Environments
File System Network Process

53. Isolated
Environments
User
Container
Application
File System Network Process

54. Streams & Signals

55. STDO
UT/S
TDER
R
CLI
User
App
STDIN

56. STDO
UT/S
TDER
R
CLI
User
App
STDIN
STDOUT &
STDERR
STDIN
Another
App

57. STDO
UT/S
TDER
R
CLI
User
App
STDIN
STDOUT &
STDERR
STDIN
Another
App

58. Mixlib::Shellout
> ls = Mixlib::ShellOut.new("ls")
> ls.run_command
> ls.stdout
“init.elnREADME.mdn”
Nikhil Mungel
www.hyfather.com @hyfather

59. Mixlib::Shellout
> ls = Mixlib::ShellOut.new("ls")
> ls.run_command
> ls.stdout
“init.elnREADME.mdn”
Nikhil Mungel
www.hyfather.com @hyfather

60. Nikhil Mungel
www.hyfather.com @hyfather

61. IO#tty?
Nikhil Mungel
www.hyfather.com @hyfather

62. Output
$stdout TRACE DEBUG INFO
$stderr WARN ERROR FATAL
Nikhil Mungel
www.hyfather.com @hyfather

63. Thanks!
I am currently a Grad Student at
San Jose State
Formerly at ThoughtWorks Studios
slidesha.re/rubycli
Nikhil Mungel
www.hyfather.com @hyfather