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Snippets for yer computer needs

Ruby

CLI

# Print warnings
ruby -w ...

# get machine instructions
ruby --dump insns script.rb

# See how commands are parsed
ruby --dump parsetree_with_comment script.rb

Syntax cheatsheet

class Thing
  attr_accessor :foo
  def initialize(foo = 0)
    @foo = foo
  end

  # use `self.` to define a class method
  def self.foobar
    puts "foobar"
  end

  private

  def bar
    puts "whoa"
  end
end

if val = 42
  #do stuff
elsif val = 33
  #do stuff
else
  #do stuff
end

# Ternary operator
exp ? true : false

# Begin block
begin
  # try to do this
rescue Exception
  # oh crap
else
  # whatever else
ensure
  # do this no matter what
end

# Case statement
case thing
when 3
  puts 'fizz'
when 5
  puts 'buzz'
else
  puts thing
end

# Safe navigation operator (introduced in Ruby 2.3)
u && u.profile && u.profile.thumbnails && u.profiles.thumbnails.large
# versus
u&.profile&.thumbnails&.large

Threads

# Abort on thread errors
Thread.abort_on_exception = true

Thread.new do
  fail 'Cannot continue'
end

loop do
  sleep
end

Running processes

% Notation

Modifier Meaning
%i[ ] Non-interpolated symbol array (Ruby 2+)
%I[ ] Interpolated symbol array (Ruby 2+)
%q[ ] Non-interpolated String (except for \ [ and ])
%Q[ ] Interpolated String (default)
%r[ ] Interpolated Regexp (flags can appear after the closing delimiter)
%s[ ] Non-interpolated Symbol
%w[ ] Non-interpolated Array of words, separated by whitespace
%W[ ] Interpolated Array of words, separated by whitespace
%x[ ] Interpolated shell command

Extending and Embedding

### C

Take a look at doc/extension.rdoc in MRI

### C++

Rice

### Rust

Can use C bindings…

### Java

### Embedded C

Neat Ruby source files to look at

file desc
parse.y The lexing/parsing of Ruby source code
defs/keywords The reserved keywords of Ruby

parsing

### parsetree (CLI)

ruby --dump parsetree

This gives the names for the node objects used in ast.c/compile.c/node.c/vm.c in CRuby source (output not usable in other implementations)

### Ripper

Built-in since Ruby 1.9

Dumps S-expressions

require 'ripper'
require 'pp'

f = File.read('foo.rb')
pp Ripper.sexp(f)

http://www.rubyinside.com/using-ripper-to-see-how-ruby-is-parsing-your-code-5270.html

### ast and parser gems

### code reconstruction from AST

Ractors

Ractors are Ruby’s take on the Actor Model. The main Ruby thread is a Ractor.

ract = Ractor.new do
  puts "hello"
end

ract.take

JSON

require 'json'
obj = JSON.parse(File.read('./thing.json'))
obj.to_json
JSON.pretty_generate(obj)

Naming idioms

local_variable
@instance_variable
@@class_variable
CONSTANT_VARIABLE
ClassName
ModuleName
$global

Minitest

CSV

require 'csv'
data = CSV.read('path/to/file', headers: true)

Write to a file

fp = File.open(filename, mode)
fp.write('bloop')
fp.close

Read individual chars

fp = File.open(filename, mode)
fp.each_char do |char|
      puts char
end
fp.close

heredoc

heredoc documentation

  message1 = <<EOM
  This string starts at line start
EOM # Needs to be at 0 position

  message2 = <<-EOM
While the terminator is indented, text is left flush
  EOM

  message3 = <<~EOM
    This one removes space before first printable character 
      of the least indented line. Empty lines ignored

    Available in Ruby 2.3+
  EOM

Gems

# Build a gem
gem build name.gemspec

# upload gem to rubygems.org or other host
gem push name-0.0.1.gem [--host HOST]

# add a gem source
gem source -a SOURCE
# remove a source
gem source -r SOURCE
# update source cache
gem source -u

# add an owner
gem owner GEM --add EMAIL
# remove an owner
gem owner GEM --remove EMAIL

Environment variables:

var description
GEM_PATH where gems can be loaded
GEM_HOME where gems are installed

ObjectSpace

This module is useful for understanding the memory size of what you’re working with, as well as seeing what objects are still alive at a given time

ObjectSpace.count_objects

ObjectSpace docs

Versions

This is a list of interesting bits from Ruby versions

Rdoc

*word*
    displays word in a bold font
_word_
    displays word in an emphasized font
+word+
    displays word in a code font

Comments:

# This is the foo function
#--
# Lines between -- and ++ won't be parsed
#++
# It will return true
def foo
  true
end

Don’t document a thing:

module MyModule # :nodoc:
end

Links:

https://github.com/example/example
mailto:user@example.com
{RDoc Documentation}[http://rdoc.rubyforge.org]
{RDoc Markup}[rdoc-ref:RDoc::Markup]

Using ri on Fedora

To get the system ruby library documentation, you’ll need to install ruby-doc

sudo dnf install rubygem-rdoc ruby-doc

Get list of undocumented code

rdoc -C1 > documentation_coverage.txt

### Links

ERB

Core ERB documentation

Tags:

<% Ruby code -- inline with output %>
<%= Ruby expression -- replace with result %>
<%# comment -- ignored -- useful in testing %>
% a line of Ruby code -- treated as <% line %> (optional -- see ERB.new)
%% replaced with % if first thing on a line and % processing is used
<%% or %%> -- replace with <% or %> respectively

Trim mode:

code desc
% enables Ruby code processing for lines beginning with %
<> omit newline for lines starting with <% and ending in %>
> omit newline for lines ending in %>
- omit blank lines ending in -%>

Fibers

A fiber is an independent execution context that can be paused and resumed programmatically. There’s always a currently active fiber, which is created by the runtime for each thread. Fibers are managed in the userspace program, using cooperative multitasking (the fiber must voluntarily give up control) instead of the OS’ pre-emptive multitasking.

A fiber always starts in a suspended state, it will not run until you switch to it with #transfer.

States: :running, :waiting, :runnable, :dead

Debugging

-r debug

ruby -r debug example.rb

Irb

As of Ruby 2.4+, you can use binding.irb for an experience similar to Pry

Pry

http://pryrepl.org/

require 'pry'

# start REPL
binding.pry
# get list of commands
repl> help

# quit program
repl> !!!

Performance

As with any system performance advice, don’t forget to benchmark

Frozen string literals

When ‘freeze’ is called on a string you are marking that string as immutable. The performance benefit is that the object can be re-used without new object allocation.

def unfrozen
  a = 'hello'
  a.object_id
end

p unfrozen
p unfrozen

def frozen
  a = 'world'.freeze
  a.object_id
end

p frozen
p frozen
$ ruby freeze.rb
60
80
100
100

File pragma

In Ruby 2.3+, you can add this pragma to opt-in to all string literals being made immutable in the source file. Note - this isn’t a guaranteed performance win!

To debug, use --debug=frozen-string-literal

# frozen_string_literal: true

Performance pitfalls

Inefficient string concatenation

x = 'a'
x += 'b'
# the above is equivalent to
x = 'a'
y = x + 'b'
x = y

instead, use this:

x = 'a'
x << 'b'

Worst case, it’ll be a realloc but won’t trigger GC.

Memory-heavy iterators

When going through a file, it’s better to read the file line-by-line like the following to avoid GC hits:

file = File.open('foobar', 'r')
while line = file.gets
  line.split('.')
end

Use in-place operations whenever possible

The difference between sort and sort! can be pretty significant, especially when you’re dealing with loops and big objects, since you’re copying the object with sort. If you don’t need to re-use the value, use a mutating (!) function.

Use a time format instead of Date#parse

If you know in advance what your time format is, don’t use Date#parse, since there’s a bunch of overhead just figuring out what kind of time it is.

Other significant wins

Benchmarking

Running the profiler

ruby -r profile script.rb

Benchmarking

require 'benchmark'

n = 50000

# this gives you a Benchmark::Tms object
tms = Benchmark.measure { for i in 1..n; a = "1"; end }

# Returns [@label, @utime, @stime, @cutime, @cstime, @real]
tms.to_a

Contributing

Template for feature proposals

From contributing.rdoc:

[Abstract] Summary of your feature [Background] Describe current behavior and why it is problem. Related work, such as solutions in other language helps us to understand the problem. [Proposal] Describe your proposal in details [Details] If it has complicated feature, describe it [Usecase] How would your feature be used? Who will benefit from it? [Discussion] Discuss about this proposal. A list of pros and cons will help start discussion. [Limitation] Limitation of your proposal [Another alternative proposal] If there are alternative proposals, show them. [See also] Links to the other related resources

RubyVM

https://docs.ruby-lang.org/en/master/RubyVM.html

Conferences

async

Bundler

Writing a Gemfile

source 'https://example.org' do
  # If you have private gems, put them here so that someone doesn't spoof them on rubygems.org !
end

source 'https://rubygems.org' do
  # Gems here
end

# Using a git repository
gem 'rack', git: 'https://github.com/rack/rack'

# Make a gem group optional
# use `bundle config set --local with GROUP` to install
group :development, optional: true do
  gem 'guard'
end

https://bundler.io/v2.2/guides/git.html

Install gems to dir

bundle config set --local path 'vendor'

# Deprecated way:
bundle install --path dir

mruby

compile with mrbc

Ruby net/http

require 'net/http'

uri = URI('http://example.com')

Net::SMTP

gem source

# Gemfile
gem 'net-smtp'
# Using starttls
smtp = Net::SMTP.new smtp_options[:address], smtp_options[:port]
smtp.enable_starttls_auto
smtp.start(
  smtp_options[:helo_domain],
  smtp_options[:user_name],
  smtp_options[:password],
  smtp_options[:authentication]
) do |smtp|
  smtp.send_message msgstr, "from@example.org", [ "to@example.org" ]
end

Binary manipulation with ::Array#pack / ::String#unpack

Integer:

Directive Meaning
C 8-bit unsigned (unsigned char)
S 16-bit unsigned, native endian (uint16_t)
L 32-bit unsigned, native endian (uint32_t)
Q 64-bit unsigned, native endian (uint64_t)
c 8-bit signed (signed char)
s 16-bit signed, native endian (int16_t)
l 32-bit signed, native endian (int32_t)
q 64-bit signed, native endian (int64_t)
S_, S! unsigned short, native endian
I, I_, I! unsigned int, native endian
L_, L! unsigned long, native endian
n 16-bit unsigned, network (big-endian) byte order
N 32-bit unsigned, network (big-endian) byte order
v 16-bit unsigned, VAX (little-endian) byte order
V 32-bit unsigned, VAX (little-endian) byte order
U UTF-8 character
w BER-compressed integer (see Array.pack)
Q_, Q! unsigned long long, native endian (ArgumentError if the platform has no long long type.)
s_, s! signed short, native endian
i, i_, i! signed int, native endian
l_, l! signed long, native endian
q_, q! signed long long, native endian (ArgumentError if the platform has no long long type.)
desc suffix
native endian !
native endian _
big-endian >
little-endian <

Float:

Directive Meaning
D, d double-precision, native format
F, f single-precision, native format
E double-precision, little-endian byte order
e single-precision, little-endian byte order
G double-precision, network (big-endian) byte order
g single-precision, network (big-endian) byte order

String:

Directive Meaning
A arbitrary binary string (remove trailing nulls and ASCII spaces)
a arbitrary binary string
Z null-terminated string
B bit string (MSB first)
b bit string (LSB first)
H hex string (high nibble first)
h hex string (low nibble first)
u UU-encoded string
M quoted-printable, MIME encoding (:RFC:2045)
m base64 encoded string (:RFC:2045) (default) base64 encoded string (:RFC:4648) if followed by 0
P pointer to a structure (fixed-length string)
p pointer to a null-terminated string

Misc:

Directive Meaning
@ skip to the offset given by the length argument
X skip backward one byte
x skip forward one byte

Ruby Gems

Rack

Live reloading

# config.ru
require 'rack-livereload'
use Rack::LiveReload

(pair it with guard-livereload)

Sorbet

Home page

# First run
bundle exec srb init
# Run typechecker
bundle exec src tc

Gemfile:

gem 'sorbet', :group => :development

Sinatra

Cheatsheet

# To run a Sinatra server
ruby app.rb
require 'sinatra'
get '/helloworld' do
  'Hello, world!'
end

get '/haml' do
  # Render template views/thing, insert some variables
  haml :thing, locals: {foo: 'bar', biz: 'baz'}
end

Using Rack

Classic-style:

require './app'
run Sinatra::Application

Using haml

Reloader

http://sinatrarb.com/contrib/reloader

# Gemfile
gem install sinatra-contrib
# Classic
require "sinatra/reloader" if development?

# Specify additional load paths
also_reload '/path/to/some/file' # path can use globbing
dont_reload '/path/to/other/file'
after_reload do
  puts 'reloaded'
end

# Modular approach
require "sinatra/base"
require "sinatra/reloader"

class MyApp < Sinatra::Base
  configure :development do
    register Sinatra::Reloader
    also_reload '/path/to/some/file'
    dont_reload '/path/to/other/file'
    after_reload do
      puts 'reloaded'
    end
  end

  # ...
end

Mustache handler

Capistrano

# Create new stub
cap install

Camping

Guard

# Create bin/guard
bundle binstub guard

# Write a Guardfile
guard init

# List available guards
guard list

Integrations:

gem initializing
guard-minitest guard init minitest
guard-rubocop guard init rubocop

Rubocop

NodePattern

Note: table uses int node, but can be for any type of node.

Variable length patterns can only be used in a sequence once

syntax desc
int match int exactly
(int 1) match a node with more precision (eg, int node that represents 1)
_ match any single node
several subsequent nodes
int* Match zero or more targets of int type
int? Match zero or one of the int type
int+ Match at least one of the int type
<int float> Match integer and float in either order
{int float} “OR” union function (ie either int or float)
(int [odd? positive?]) “AND”, useful when using predicate methods against type
(int $_) Capture the node/element (variable length captured as arrays)
(^array int+) TODO Check the parent of a node
(`int int*) Check for descendents of a node, here an array of ints
(int ALLOWED_INTS) Use a constant (here ALLOWED_INTS) in a pattern

Predicate methods can be used as well:

# Patterns can have a comment, with `# ` to EOL

int_type?  # equivalent to (int _)
(int odd?) # Only match odd numbers

# `#` can be used to call an outside function

(int #prime?) # if a prime? method has been created
(int #multiple_of?(12)) # You can also use arguments in your functions (the signature here being `multiple_of?(value, multiple)`)

# An argument in the matcher can be passed to a pattern
def_node_matcher :int_node_magic_number?, '(int #magic_number?(%1))'

Developing a pattern to match (consider using irb for interactivity):

require 'rubocop'
code = '2 + 2'
source = RuboCop::ProcessedSource.new(code, RUBY_VERSION.to_f)
node = source.ast
RuboCop::NodePattern.new('(int ...)').match(node)
# Generating AST on the command line
ruby-parse -e '2 + 2'

adsf

gem install 'adsf'
gem install 'adsf-live' # Live reload functionality
adsf --live-reload

Ruby on Rails

Installing and setting up Rails 4

gem install rails
rails new app_name
cd app_name
rake db:create
rails server # (on standalone machine)
rails generate controller home index
rm public/index.html
# Uncomment the ``root :to => "home#index"`` line
$EDITOR config/routes.rb

Scaffolding

rails generate scaffold Post user:references title:string{50} content:text

Add indexes to migration

rails g resource user name:index email:uniq

Using RSpec with Rails

Add to Gemfile:

gem 'rspec-rails'
gem 'guard-rspec'
rails generate rspec:install

ActiveRecord

Supported database column types:

Use “AddColumnToTable” style migration names to have the work done for you automatically in the migration

Validating Active Records

class Post < ActiveRecord::Base
  # ...

  validates :name,  :presence => true
  validates :title, :presence => true,
       				 :length => { :minimum => 5 }
end

Ensure uniqueness at the db level

  1. rails generate migration add_index_to_users_email
  2. add to migration file under def change: add_index :users, :email, unique: true
  3. bundle exec rake db:migrate

Database

# Migrate to new model
rake db:migrate

# Return to previous model
rake db:rollback

Automated testing with guard and spork

group :test, :development do
  gem 'guard-spork'
  gem 'spork'
  gem 'guard-rspec'
end
group :test do
  gem 'rb-inotify'
  gem 'libnotify'
end
bundle exec guard init rspec
bundle exec spork --bootstrap
bundle exec guard init spork

Creating tables

create_table "contacts" do |t|
  t.integer  "user_id", :null => false
  t.string   "name", :null => false
  t.string   "phone", :limit => 40
  t.string   "email"
end

Reset test database

bundle exec rake db:test:prepare

Rake default niceties

# Find TODO, FIXME, and OPTIMIZE comment tags
rake notes

# Get versions
rake about

Simple wins

Omniauth

These notes are assuming you’re also allowing regular email/password logins. It’s greatly simplified if you don’t…

rails generate model Authorization provider:string uid:string user_id:integer

Gemfile:

gem 'omniauth'
gem 'omniauth-twitter'
gem 'omniauth-facebook'
gem 'omniauth-linkedin'

config/initializers/omniauth.rb:

	Rails.application.config.middleware.use OmniAuth::Builder do
	  provider :twitter, 'CONSUMER_KEY', 'CONSUMER_SECRET'
	  provider :facebook, 'APP_ID', 'APP_SECRET'
	  provider :linked_in, 'CONSUMER_KEY', 'CONSUMER_SECRET'
	end

app/models/user.rb:

has_many :authorizations

def add_provider(auth_hash)
  unless authorizations.find_by_provider_and_uid(auth_hash["provider"], auth_hash["uid"])
        Authorization.create :user => self, :provider => auth_hash["provider"], :uid => auth_hash["uid"]
  end
end

app/controllers/sessions_controller.rb:

def omniauth_create
  auth_hash = request.env['omniauth.auth']
  if session[:user_id]
        # Means user is signed in. Add the authorization to the user
        user = User.find(session[:user_id])
        user.add_provider(auth_hash)
  else
        auth = Authorization.find_or_create(auth_hash)
        # Create the session
        session[:user_id] = auth.user_id
        user = User.find(session[:user_id])
  end
  sign_in user
  redirect_back_or user
end

app/models/authorization.rb:

belongs_to :user
validates :provider, :uid, :presence => true

def self.find_or_create(auth_hash)
  unless auth = find_by_provider_and_uid(auth_hash["provider"], auth_hash["uid"])
        user = User.find_by_email(auth_hash["info"]["email"])
        if not user
          # If it's a new user, we want to give them a solid password
          random_string = SecureRandom.base64(30)
          user = User.create :name => auth_hash["info"]["name"],
       					   :email => auth_hash["info"]["email"],
       					   :password => random_string,
       					   :password_confirmation => random_string
        end
        auth = create :user_id => user, :provider => auth_hash["provider"], :uid => auth_hash["uid"]
  end
  auth
end

config/routes.rb:

match '/auth/:provider/callback', to: 'sessions#create'
match '/auth/failure', to: 'sessions#failure'

Gravatar

Helper to return Gravatar image:

# Returns the Gravatar (http://gravatar.com/) for the given user.
def gravatar_for(user, options = { size: 50 })
  gravatar_id = Digest::MD5::hexdigest(user.email.downcase)
  size = options[:size]
  gravatar_url = "https://secure.gravatar.com/avatar/#{gravatar_id}?s=#{size}"
  image_tag(gravatar_url, alt: user.name, class: "gravatar")
end

Ruby-Next

RVM

curl -L https://get.rvm.io | bash -s stable --ruby

# Installing openssl and readline for dependencies
curl -L https://get.rvm.io | bash -s stable
rvm pkg install openssl
rvm pkg install readline
rvm install 1.9.3 --with-openssl-dir=$HOME/.rvm/ --with-readline-dir=$HOME/.rvm/usr

# Create a per-project rvmrc
rvm --rvmrc --create 1.9.3@projectname
# set default ruby
rvm --default use 2.2.0
# Use a gemset
rvm gemset [create|use|delete] gemsetname
# See gem directory
gem env gemdir

For automatic gemset initialization, add gems to ~/.rvm/gemsets/global.gems