The document describes a presentation on crafting beautiful command line applications using Ruby. The presentation discusses why the command line is useful, what makes a good CLI app, and some key principles for CLI apps like least astonishment, reversibility, config files, graceful failure, and honoring piping. It also covers input/output in CLI apps and libraries like OptionParser, Mixlib::CLI, and Thor that can help build CLI apps in Ruby.

1. RubyConf India 2012
Pune
Crafting Beautiful
Command Line Applications
using Ruby
Shishir Nikhil
@shishirdas @hyfather

2. Shishir Das
@shishirdas
ThoughtWorks

3. Nikhil Mungel
@hyfather
ThoughtWorks

4. Why the command line?

5. Why the command line?

14. ey
heroku knife
puppet
pg_ctl mysql rails
git

15. bash zsh powershell
ey
heroku knife
puppet
pg_ctl mysql rails
git

16. ey
heroku knife
puppet
pg_ctl mysql rails
git
Developers
and
QAs

17. Lightweight

18. Lightweight

19. Scriptable

20. Consistent UX

21. Consistent UX
*

22. What makes a CLI app
good?

23. The Luxury of
Ignorance

24. ~ > rails

25. ~ > rails
Usage: rails COMMAND [ARGS]
The most common rails commands are:
generate Generate new code (short-cut alias: "g")
console Start the Rails console (short-cut alias: "c")
server Start the Rails server (short-cut alias: "s")
~ >

26. ~ > rails generate

27. ~ > rails generate
Usage: rails generate GENERATOR [args] [options]
Please choose a generator below.
Rails:
assets
controller
generator
helper
integration_test
mailer
migration
model
observer
performance_test
plugin
~ >

28. ~ > ssh

29. ~ > ssh
usage: ssh [-1246AaCfgKkMNnqsTtVvXxYy] [-b bind_address] [-c
cipher_spec]
[-D [bind_address:]port] [-F configfile]
[-I pkcs11] [-i identity_file]
[-L [bind_address:]port:host:hostport]
[-l login_name] [-O ctl_cmd] [-o option] [-p port]
[-R [bind_address:]port:host:hostport] [-S ctl_path]
[-W host:port] [-w local_tun[:remote_tun]]
[user@]hostname [command]
~ >

30. Least Astonishment

31. ~ > bundle

32. ~ > bundle
Fetching source index for https://rubygems.org/
Using rake (0.9.2.2)
Installing i18n (0.6.0)
Installing multi_json (1.0.4)
Installing activesupport (3.2.1)
Installing builder (3.0.0)
Installing activemodel (3.2.1)
Installing erubis (2.7.0)
~ >

33. Reversibility

34. ~ > git commit -am "Added a new framework"

35. ~ > git commit -am "Added a new framework"
[master b4a2130] Added a new framework
2 files changed, 1012 insertions(+), 529 deletions(-)
~ >

36. ~ > git commit -am "Added a new framework"
[master b4a2130] Added a new framework
2 files changed, 1012 insertions(+), 529 deletions(-)
~ > git reset HEAD^

37. ~ > git commit -am "Added a new framework"
[master b4a2130] Added a new framework
2 files changed, 1012 insertions(+), 529 deletions(-)
~ > git reset HEAD^
Unstaged changes after reset:
M javascript/framework.js
M javascripts/support.js
~ >

38. Config Files

39. ~ > knife cookbook upload apache2 -o /User/foo/cookbooks --
server-url http://chef-server:4000 --key /etc/chef/my.key --color
~ >

40. ~ > knife cookbook upload apache2 -o /User/foo/cookbooks --
server-url http://chef-server:4000 --key /etc/chef/my.key --color
~ >
~ > cat knife.rb
log_level :info
log_location STDOUT
node_name 'blitz'
client_key '/Users/shishir/.chef/blitz.pem'
validation_client_name 'chef-validator'
validation_key '/etc/chef/validation.pem'
chef_server_url 'http://10.10.100.202:4000'
cache_type 'BasicFile'
cache_options( :path => '/Users/shishir/.chef/checksums' )
~ >

41. ~ > knife cookbook upload apache2 -o /User/foo/cookbooks --
server-url http://chef-server:4000 --key /etc/chef/my.key --color
~ >
~ > cat knife.rb
log_level :info
log_location STDOUT
node_name 'blitz'
client_key '/Users/shishir/.chef/blitz.pem'
validation_client_name 'chef-validator'
validation_key '/etc/chef/validation.pem'
chef_server_url 'http://10.10.100.202:4000'
cache_type 'BasicFile'
cache_options( :path => '/Users/shishir/.chef/checksums' )
~ >
~ > knife cookbook upload apache2

42. Graceful Failure

43. ~ > git pull

44. ~ > git pull
You asked me to pull without telling me which branch you
want to merge with, and 'branch.master.merge' in
your configuration file does not tell me, either. Please
specify which branch you want to use on the command line and
try again (e.g. 'git pull <repository> <refspec>').
See git-pull(1) for details.
If you often merge with the same branch, you may want to
use something like the following in your configuration file:
[branch "master"]
remote = <nickname>
merge = <remote-ref>
[remote "<nickname>"]
url = <url>
fetch = <refspec>
See git-config(1) for details.

45. No hidden states

48. Confirmations should
be scriptable

49. ~ > gem uninstall rspec

50. ~ > gem uninstall rspec
You have requested to uninstall the gem:
rspec-2.8.0
cucumber-1.1.4 depends on [rspec (>= 2.7.0)]
If you remove this gems, one or more dependencies will not be met.
Continue with Uninstall? [Yn] n

51. ~ > gem uninstall rspec
You have requested to uninstall the gem:
rspec-2.8.0
cucumber-1.1.4 depends on [rspec (>= 2.7.0)]
If you remove this gems, one or more dependencies will not be met.
Continue with Uninstall? [Yn] n
~ > gem uninstall -I rspec

52. ~ > gem uninstall rspec
You have requested to uninstall the gem:
rspec-2.8.0
cucumber-1.1.4 depends on [rspec (>= 2.7.0)]
If you remove this gems, one or more dependencies will not be met.
Continue with Uninstall? [Yn] n
~ > gem uninstall -I rspec
Successfully uninstalled rspec-2.8.0

53. Honor Piping

56. IO#tty?

57. Why Ruby?

58. Scripting Language

59. Easy text
manipulation

60. Good Abstractions

61. Plethora of gems to
help you

62. Examples to learn
from

63. Structure of CLI
apps

65. Input Execution Output

66. Input Execution Output
STDIO = UI/UX

67. Input

68. Input
STDIN

69. Input
ARGV/ENV
STDIN

70. Input
ARGV/ENV
STDIN

71. Input
ARGV/ENV
STDIN

72. Input
OptionParser
ARGV/ENV
STDIN

73. Input
OptionParser
ARGV/ENV
STDIN

74. Input Libraries
OptionParser
ARGV/ENV
STDIN

75. 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!

76. 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

77. 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

78. 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

79. 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

80. The Mixlib Suite

81. 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

82. 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

83. 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

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

85. 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’

86. 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’

87. Thor

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

89. 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

90. 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

91. 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

92. 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

93. 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

94. 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

95. 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

96. Testing

98. Input Execution Output

99. Input Execution Output

100. Input Execution Output
Mostly third party libraries

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

102. Input Execution Output
System

103. System
File System Network Process

104. Isolated
Environments
Container
User Application
File
Memory Processes
System

105. Streams & Signals

106. STDOUT
STDIN
App
STDERR

107. STDOUT
STDIN
App
STDERR

108. STDOUT
STDIN
App
STDERR
STDOUT & STDERR
STDIN
App

109. Mixlib::Shellout
> ls = Mixlib::ShellOut.new("ls")
> ls.run_command
> ls.stdout
“init.elnREADME.mdn”

110. Mixlib::Shellout
> ls = Mixlib::ShellOut.new("ls")
> ls.run_command
> ls.stdout
“init.elnREADME.mdn”

111. Plugin Architecture

112. Hooks

113. Logging

114. GNU CLI standards
‘--version’ and ‘--help’
Input/Output Files --
-O for Output Files

115. “CLI apps could be
the first consumers
”
of your services.

116. “CLI apps could be
the first consumers
”
of your services.

117. “CLI apps could be
the first consumers
”
of your services.
Testing Development
Cheap
No rich UI,
functional
Fast
tests

118. Ideas
CLI app for a REST API: Github
SCM Plugins for Knife
Transform Rake scripts into first
class CLI apps
Shishir Nikhil
@shishirdas @hyfather

119. Questions
Comments
Suggestions
Shishir Nikhil
@shishirdas @hyfather