Crafting Beautiful CLI Applications in Ruby

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

Shishir Das@shishirdasThoughtWorks

Nikhil Mungel@hyfatherThoughtWorks

Why the command line?

eyheroku knife puppet pg_ctl mysql rails git

bash zsh powershell eyheroku knife puppet pg_ctl mysql rails git

eyheroku knife puppet pg_ctl mysql rails git Developers and QAs

Lightweight

Scriptable

Consistent UX

Consistent UX *

What makes a CLI app good?

The Luxury of Ignorance

~ > rails

~ > railsUsage: 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")~ >

~ > rails generate

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

~ > ssh

~ > sshusage: ssh [-1246AaCfgKkMNnqsTtVvXxYy] [-b bind_address] [-ccipher_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]~ >

Least Astonishment

~ > bundle

~ > bundleFetching 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)~ >

Reversibility

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

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

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

~ > 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.jsM javascripts/support.js~ >

Config Files

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

~ > 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 :infolog_location STDOUTnode_name blitzclient_key /Users/shishir/.chef/blitz.pemvalidation_client_name chef-validatorvalidation_key /etc/chef/validation.pemchef_server_url http://10.10.100.202:4000cache_type BasicFilecache_options( :path => /Users/shishir/.chef/checksums )~ >

~ > 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 :infolog_location STDOUTnode_name blitzclient_key /Users/shishir/.chef/blitz.pemvalidation_client_name chef-validatorvalidation_key /etc/chef/validation.pemchef_server_url http://10.10.100.202:4000cache_type BasicFilecache_options( :path => /Users/shishir/.chef/checksums )~ >~ > knife cookbook upload apache2

Graceful Failure

~ > git pull

~ > git pullYou asked me to pull without telling me which branch youwant to merge with, and branch.master.merge inyour configuration file does not tell me, either. Pleasespecify which branch you want to use on the command line andtry again (e.g. git pull <repository> <refspec>).See git-pull(1) for details.If you often merge with the same branch, you may want touse 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.

No hidden states

Confirmations should be scriptable

~ > gem uninstall rspec

~ > gem uninstall rspecYou have requested to uninstall the gem: rspec-2.8.0cucumber-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 rspecYou have requested to uninstall the gem: rspec-2.8.0cucumber-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

~ > gem uninstall rspecYou have requested to uninstall the gem: rspec-2.8.0cucumber-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 rspecSuccessfully uninstalled rspec-2.8.0

Honor Piping

IO#tty?

Why Ruby?

Scripting Language

Easy textmanipulation

Good Abstractions

Plethora of gems to help you

Examples to learn from

Structure of CLI apps

Input Execution Output

Input Execution Output STDIO = UI/UX

Input STDIN

Input ARGV/ENV STDIN

Input OptionParser ARGV/ENV STDIN

Input Libraries OptionParser ARGV/ENV STDIN

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

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

The Mixlib Suite

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

config.rbserver_url “http://server.remote”username “elvis”password “hotdog”

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

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

class Test < Thor desc " FILE", "an example task" method_option :delete, :aliases => "-d", :desc => "Delete the file" def example(file) endend~ > myapp help test:exampleUsage: thor test:example FILEOptions: -d, [--delete=DELETE] # Delete the file after parsing itan example task

Testing

Input Execution Output

Input Execution OutputMostly third party libraries

Input Execution OutputTest::Unit, rspec etc.

Input Execution Output System

SystemFile System Network Process

Isolated Environments ContainerUser Application File Memory Processes System

Streams & Signals

STDOUTSTDIN App STDERR

STDOUTSTDIN App STDERR STDOUT & STDERR STDIN App

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

Plugin Architecture

Logging

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

“CLI apps could bethe first consumers ” of your services.

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

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

Questions Comments SuggestionsShishir Nikhil@shishirdas @hyfather

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Crafting Beautiful CLI Applications in Ruby

by Nikhil Mungel

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