10 Things You Didn't Know Ruby Could do

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10 Things You Didn’t Know Ruby Could Do

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James Edward Gray II ✤ I’m a regular on the Ruby Rogues podcast ✤ I’ve written a lot of documentation and code for Ruby ✤ This is my ﬁrst time in Hawai’i

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10 Things You Didn’t Know Rails Could Do RailsConf 2012

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10 Things You Didn’t Know Rails Could Do RailsConf 2012 42

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10 Things You Didn’t Know Ruby Could Do

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10 Things You Didn’t Know Ruby Could Do 42

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10 Things You Didn’t Know Ruby Could Do 42 101

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MRI Ruby 1.9.3-p194…

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Compiler Tricks

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#1 Ruby Can Read Your Email Or any other text content with Ruby code in it Dear Rubyists: Did you know that Ruby can even read your emails? #!/usr/bin/env ruby -w puts "It's true." __END__ I told you it could. James Edward Gray II

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puts DATA.read __END__ This is data! #2 From David Brady Storing Data in Your Code Or is it DATA?

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puts DATA.read __END__ This is data! #2 From David Brady Storing Data in Your Code Or is it DATA?

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puts DATA.read __END__ This is data! #2 From David Brady Storing Data in Your Code Or is it DATA?

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puts DATA.read __END__ This is data! #2 From David Brady Storing Data in Your Code Or is it DATA? This is data!

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DATA.rewind puts DATA.read __END__ #3 From David Brady A Cheat of a Quine Most quine rules disallow using IO

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DATA.rewind puts DATA.read __END__ #3 From David Brady A Cheat of a Quine Most quine rules disallow using IO

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DATA.rewind puts DATA.read __END__ #3 From David Brady A Cheat of a Quine Most quine rules disallow using IO DATA.rewind puts DATA.read __END__

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#4 From Ara T. Howard There Can Be Only One Use a tricky lock to make your script exclusive DATA.flock(File::LOCK_EX | File::LOCK_NB) or abort "Already running." trap("INT", "EXIT") puts "Running..." loop do sleep end __END__ DO NOT DELETE: used for locking $ ruby lock.rb Running... ^Z [1]+ Stopped ruby lock.rb $ ruby lock.rb Already running. $ fg ruby lock.rb ^C$ ruby lock.rb Running...

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#5 Your Source File, The Database A dirty trick to carry some data with the code pos = DATA.pos list = DATA.readlines if ARGV.empty? puts list.shift else list.push(*ARGV) end DATA.reopen(__FILE__, "r+") DATA.truncate(pos) DATA.seek(pos) DATA.puts list __END__ Service-Oriented Design with Ruby and Rails Practical Object-Oriented Design in Ruby $ ruby reading_list.rb \ 'Service-Oriented Design with Ruby and Rails' \ 'Practical Object-Oriented Design in Ruby' $ ruby reading_list.rb Service-Oriented Design with Ruby and Rails $ ruby reading_list.rb Practical Object-Oriented Design in Ruby

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#6 From Eric Hodel See How Ruby Reads Your Code All you have to do is ask $ ruby -e 'puts { is_this_a_block }' --dump parsetree ########################################################### ## Do NOT use this node dump for any purpose other than ## ## debug and research. Compatibility is not guaranteed. ## ########################################################### # @ NODE_SCOPE (line: 1) # +- nd_tbl: (empty) # +- nd_args: # | (null node) # +- nd_body: # @ NODE_ITER (line: 1) # +- nd_iter: # | @ NODE_FCALL (line: 1) # | +- nd_mid: :puts # | +- nd_args: # | (null node) …

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#7 From Eric Hodel Available With Comments Ruby can even explain it to you $ ruby -e 'puts { is_this_a_block }' --dump parsetree_with_comment … # @ NODE_ITER (line: 1) # | # method call with block # | # format: [nd_iter] { [nd_body] } # | # example: 3.times { foo } # +- nd_iter (iteration receiver): # | @ NODE_FCALL (line: 1) # | | # function call # | | # format: [nd_mid]([nd_args]) # | | # example: foo(1) # | +- nd_mid (method id): :puts # | +- nd_args (arguments): # | (null node) …

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#8 From Eric Hodel View the Machine Instructions Alternately, you can view the virtual machine instructions $ ruby -e 'ft = 40 + 2; p ft' --dump insns == disasm: @-e>====================== local table (size: 2, argc: 0 [opts: 0, rest: -1, post: 0, block: -1] s1) [ 2] ft 0000 trace 1 ( 1) 0002 putobject 40 0004 putobject 2 0006 opt_plus 0008 setdynamic ft, 0 0011 trace 1 0013 putself 0014 getdynamic ft, 0 0017 send :p, 1, nil, 8, 0023 leave

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#9 From Eric Hodel Watch Ruby’s Parser Work See how parse.y thinks $ ruby -e 'arg = ARGV.shift or abort "No arg"' --dump yydebug Starting parse Entering state 0 Reducing stack by rule 1 (line 782): -> $$ = nterm $@1 () Stack now 0 Entering state 2 Reading a token: Next token is token tIDENTIFIER () Shifting token tIDENTIFIER () Entering state 35 Reading a token: Next token is token '=' () Reducing stack by rule 474 (line 4275): $1 = token tIDENTIFIER () -> $$ = nterm user_variable () Stack now 0 2 …

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#10 From Eric Hodel Inspecting the Source For those of us who belong to “The Ridiculous Church of 80-Character Lines” SCRIPT_LINES__ = { } require_relative "better_be_well_formed_code" # format: {"file_name.rb" => ["line 1", "line 2", ...]} if SCRIPT_LINES__.values.flatten.any? { |line| line.size > 80 } abort "Clean up your code first!" end

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#11 From Aaron Patterson Tail Call Optimization Yeah, it’s in there def factorial(n, result = 1) if n == 1 result else factorial(n - 1, n * result) end end p factorial(30_000)

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#11 From Aaron Patterson Tail Call Optimization Yeah, it’s in there def factorial(n, result = 1) if n == 1 result else factorial(n - 1, n * result) end end p factorial(30_000) /…/factorial.rb:2: stack level too deep (SystemStackError)

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RubyVM::InstructionSequence.compile_option = { tailcall_optimization: true, trace_instruction: false } eval <

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RubyVM::InstructionSequence.compile_option = { tailcall_optimization: true, trace_instruction: false } eval <

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RubyVM::InstructionSequence.compile_option = { tailcall_optimization: true, trace_instruction: false } eval <

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RubyVM::InstructionSequence.compile_option = { tailcall_optimization: true, trace_instruction: false } eval <

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Syntax

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#12 Pass Some Arguments Up Helps add functionality to methods class Parent def show_args(*args) p args end end class Child < Parent def show_args(a, b, c) super(a, b) end end Child.new.show_args(:a, :b, :c)

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#13 From Daniel Azuma Pass The Same Arguments Up Remember, super is a magical keyword class Parent def show_args(*args, &block) p [*args, block] end end class Child < Parent def show_args(a, b, c) super end end Child.new.show_args(:a, :b, :c) { :block }

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#14 From Daniel Azuma Pass Modified Arguments Up Scary magic class Parent def show_args(*args) p args end end class Child < Parent def show_args(a, b, c) a.upcase! # not too surprising b = "Wow!" # very surprising super end end Child.new.show_args("a", "b", "c")

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#15 From Daniel Azuma Pass No Arguments Up The parentheses are required class Parent def show_args(*args) p args end end class Child < Parent def show_args(a, b, c) super() end end Child.new.show_args(:a, :b, :c)

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#16 From Marten Veldthuis Pass No Block Up How to make a block disappear class Parent def show_block(&block) p block end end class Child < Parent def show_block super(&nil) end end Child.new.show_block { :block }

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#17 From Avdi Grimm Asking If You Can Pass Up Ruby will tell you if a parent method is available to delegate to class DontDelegateToMe; end class DelegateToMe; def delegate; "DelegateToMe" end end module DelegateIfICan def delegate if defined? super "Modified: #{super}" else "DelegateIfICan" end end end puts DelegateToMe.new.extend(DelegateIfICan).delegate puts DontDelegateToMe.new.extend(DelegateIfICan).delegate

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#18 Lambda Literals Also known as the “stabby lambda” minimal = -> { p :called } minimal.call loaded = ->(arg, default = :default, &block) { p [arg, default, block] } loaded.call(:arg) { :block }

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#18 Lambda Literals Also known as the “stabby lambda” minimal = -> { p :called } minimal.call loaded = ->(arg, default = :default, &block) { p [arg, default, block] } loaded.call(:arg) { :block }

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#18 Lambda Literals Also known as the “stabby lambda” minimal = -> { p :called } minimal.call loaded = ->(arg, default = :default, &block) { p [arg, default, block] } loaded.call(:arg) { :block }

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#18 Lambda Literals Also known as the “stabby lambda” minimal = -> { p :called } minimal.call loaded = ->(arg, default = :default, &block) { p [arg, default, block] } loaded.call(:arg) { :block } :called [:arg, :default, #]

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#19 From Benjamin Fleischer Or Make Your Own UTF-8 Syntax Perl 6 has nothing on us # encoding: UTF-8 module Kernel alias_method :λ, :lambda end l = λ { p :called } l.call

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#19 From Benjamin Fleischer Or Make Your Own UTF-8 Syntax Perl 6 has nothing on us # encoding: UTF-8 module Kernel alias_method :λ, :lambda end l = λ { p :called } l.call

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#19 From Benjamin Fleischer Or Make Your Own UTF-8 Syntax Perl 6 has nothing on us # encoding: UTF-8 module Kernel alias_method :λ, :lambda end l = λ { p :called } l.call

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#19 From Benjamin Fleischer Or Make Your Own UTF-8 Syntax Perl 6 has nothing on us # encoding: UTF-8 module Kernel alias_method :λ, :lambda end l = λ { p :called } l.call :called

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#20 Blocks Can Now Take Blocks This trick helps with metaprogramming var = :var object = Object.new object.define_singleton_method(:show_var_and_block) do |&block| p [var, block] end object.show_var_and_block { :block }

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#21 The New Call Anything Syntax Or should we call it the “Call Me Maybe” syntax? class Callable def call :my_own_class end end p -> { :lambda }.() p [ ].method(:class).() p Callable.new.()

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#21 The New Call Anything Syntax Or should we call it the “Call Me Maybe” syntax? class Callable def call :my_own_class end end p -> { :lambda }.() p [ ].method(:class).() p Callable.new.()

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#21 The New Call Anything Syntax Or should we call it the “Call Me Maybe” syntax? class Callable def call :my_own_class end end p -> { :lambda }.() p [ ].method(:class).() p Callable.new.() :lambda Array :my_own_class

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#22 From David Brady Symbol#to_proc Takes Arguments This probably isn’t a great thing to abuse, but still… shiny to_s_proc = :to_s.to_proc # or: lambda(&:to_s) receiver = 255 arg = 16 puts to_s_proc[receiver, arg]

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#23 inject() a Symbol This is even shorter than using Symbol#to_proc p (1..10).inject(:*) # instead of: inject(&:*)

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#23 inject() a Symbol This is even shorter than using Symbol#to_proc p (1..10).inject(:*) # instead of: inject(&:*)

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#23 inject() a Symbol This is even shorter than using Symbol#to_proc p (1..10).inject(:*) # instead of: inject(&:*) 3628800

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#24 From Piotr Szotkowski Case on Ranges Case statements work with anything that deﬁnes ===, like Range age = rand(1..100) p age case age when -Float::INFINITY..20 puts "You're too young." when 21..64 puts "You are the right age." when 65..Float::INFINITY puts "You're too old." end

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#25 From Piotr Szotkowski Case on Date Ranges Range objects work in a case and Date objects work as a Range endpoint require "date" start_of_aloha_ruby_conf = Date.new(2012, 10, 8) end_of_aloha_ruby_conf = Date.new(2012, 10, 9) case Date.today when Date.new...start_of_aloha_ruby_conf puts "Anticipation is building." when start_of_aloha_ruby_conf..end_of_aloha_ruby_conf puts "Mind being blown." when (end_of_aloha_ruby_conf + 1)..Date::Infinity puts "You've learned some Ruby while in paradise." end

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require "prime" n = rand(1..10) p n case n when lambda(&:prime?) puts "This number is prime." when lambda(&:even?) puts "This number is even." else puts "This number is odd." end #26 From Piotr Szotkowski Case on Lambdas As of Ruby 1.9, lambdas (Proc objects) also deﬁne ===

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#27 From Benjamin Fleischer A Formatted Output Syntax Like sprintf(), but even shorter def debug(name, content) puts "%s: %p" % [name, content] end debug "Num", 42 debug "Objects", {"Grays" => %w[James Dana Summer]}

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#28 Or By Name A Ruby 1.9 enhancement to these format patterns order = {"Item 1" => 10, "Item 2" => 19.99, "Item 3" => 4.50} item_size = (["Item"] + order.keys).map(&:size).max price_size = ( ["Price".size] + order.values.map { |price| ("$%.2f" % price).size } ).max puts "%-#{item_size}s | %#{price_size}s" % {item: "Item", price: "Price"} puts "-" * (item_size + price_size + 3) order.each do |item, price| puts "%-#{item_size}s | $%#{price_size - 1}.2f" % {item: item, price: price} end

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#29 Multiple HEREDOC’s Ruby is smart enough to pick several off the same line def create_post(title, summary, body) # ... end create_post("Aloha RubyConf", <

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#29 Multiple HEREDOC’s Ruby is smart enough to pick several off the same line def create_post(title, summary, body) # ... end create_post("Aloha RubyConf", <

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#29 Multiple HEREDOC’s Ruby is smart enough to pick several off the same line def create_post(title, summary, body) # ... end create_post("Aloha RubyConf", <

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#30 Dodging a Warning The “or equals” operator includes a deﬁned? check $VERBOSE = true class WarnMe def var @var || 42 end end p WarnMe.new.var

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#30 Dodging a Warning The “or equals” operator includes a deﬁned? check $VERBOSE = true class WarnMe def var @var || 42 end end p WarnMe.new.var

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#30 Dodging a Warning The “or equals” operator includes a deﬁned? check $VERBOSE = true class WarnMe def var @var || 42 end end p WarnMe.new.var

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#30 Dodging a Warning The “or equals” operator includes a deﬁned? check $VERBOSE = true class WarnMe def var @var || 42 end end p WarnMe.new.var /…/dodging_a_warning.rb:5: warning: instance variable @var not initialized 42

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#30 Dodging a Warning The “or equals” operator includes a deﬁned? check $VERBOSE = true class WarnMe def var @var ||= 42 end end p WarnMe.new.var

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#30 Dodging a Warning The “or equals” operator includes a deﬁned? check $VERBOSE = true class WarnMe def var @var ||= 42 end end p WarnMe.new.var

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#30 Dodging a Warning The “or equals” operator includes a deﬁned? check $VERBOSE = true class WarnMe def var @var ||= 42 end end p WarnMe.new.var 42

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#31 From Pete Higgins Shortcut Variable Interpolation The braces are optional with a sigil toting variable @instance = :instance @@class = :class $global = :global puts "#@instance, #@@class, and #$global variables don't need braces."

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#32 From Michael Foley Variables From a Regex It must be a literal regex and it must be on the left side of the match operator if /\A(?\w+),\s*(?\w+)\z/ =~ "Gray, James" puts "#{first} #{last}" end

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#32 From Michael Foley Variables From a Regex It must be a literal regex and it must be on the left side of the match operator if /\A(?\w+),\s*(?\w+)\z/ =~ "Gray, James" puts "#{first} #{last}" end

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#32 From Michael Foley Variables From a Regex It must be a literal regex and it must be on the left side of the match operator if /\A(?\w+),\s*(?\w+)\z/ =~ "Gray, James" puts "#{first} #{last}" end James Gray

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#33 From Paul Battley The Unused Variable Ruby supports the convention of _ as an unused variable name [ ["James", "Gray", 36], ["Dana", "Gray", 37], ["Summer", "Gray", 2] ].each do |name, ignore, ignore| puts name end

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Data Structures

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#34 From Nathaniel Barnes Objects Can Contain Themselves Array Inception ring = [:one, [:two, [:three]]] ring.last.last << ring position = ring 4.times do puts position.first position = position.last end

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#35 Or Just Use cycle() Ruby 1.9 has a nice new repeating iterator ring = %w[one two three].cycle puts ring.take(4)

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#35 Or Just Use cycle() Ruby 1.9 has a nice new repeating iterator ring = %w[one two three].cycle puts ring.take(4)

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#35 Or Just Use cycle() Ruby 1.9 has a nice new repeating iterator ring = %w[one two three].cycle puts ring.take(4)

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#35 Or Just Use cycle() Ruby 1.9 has a nice new repeating iterator ring = %w[one two three].cycle puts ring.take(4) one two three one

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#36 Associative Arrays An ordered (by your criteria) Hash-like thing aa = [ %w[James Gray], %w[Yukihiro Matsumoto] ] p aa.assoc("James") p aa.rassoc("Matsumoto")

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#36 Associative Arrays An ordered (by your criteria) Hash-like thing aa = [ %w[James Gray], %w[Yukihiro Matsumoto] ] p aa.assoc("James") p aa.rassoc("Matsumoto")

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#36 Associative Arrays An ordered (by your criteria) Hash-like thing aa = [ %w[James Gray], %w[Yukihiro Matsumoto] ] p aa.assoc("James") p aa.rassoc("Matsumoto") ["James", "Gray"] ["Yukihiro", "Matsumoto"]

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#37 More Than Two Fields Sneak some extra data through on the end many_fields = [ %w[James Gray Developer JEG2], %w[Yukihiro Matsumoto Language\ Designer yukihiro_matz] ] first, last, title, twitter = many_fields.assoc("Yukihiro") puts "matz is a #{title}" first, last, title, twitter = many_fields.rassoc("Gray") puts "I am a #{title}"

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#38 From David Brady With Versioned Data This data structure naturally handles versioning dana = [[:first, "Dana"], [:last, "Payne"]] maiden = dana.assoc(:last).last puts "Dana's maiden name was #{maiden}." dana.unshift([:last, "Gray"]) married = dana.assoc(:last).last puts "Dana's married name is #{married}." current = dana.assoc(:last) previous = dana[(dana.index(current) + 1)..-1].assoc(:last).last puts "Dana's previous last name was #{previous}."

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#39 From Benjamin Fleischer Easy, Fast Memoization Ruby’s Hash is a memoization algorithm in disguise fibonacci = Hash.new { |numbers, index| numbers[index] = fibonacci[index - 2] + fibonacci[index - 1] }.update(0 => 0, 1 => 1) p fibonacci[300]

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#40 From Adam Williams Autovivification It’s not just for Perl programs deep = Hash.new { |hash, key| hash[key] = Hash.new(&hash.default_proc) } deep[:a][:b][:c] = 42 p deep

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#40 From Adam Williams Autovivification It’s not just for Perl programs deep = Hash.new { |hash, key| hash[key] = Hash.new(&hash.default_proc) } deep[:a][:b][:c] = 42 p deep

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#40 From Adam Williams Autovivification It’s not just for Perl programs deep = Hash.new { |hash, key| hash[key] = Hash.new(&hash.default_proc) } deep[:a][:b][:c] = 42 p deep

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#40 From Adam Williams Autovivification It’s not just for Perl programs deep = Hash.new { |hash, key| hash[key] = Hash.new(&hash.default_proc) } deep[:a][:b][:c] = 42 p deep {:a=>{:b=>{:c=>42}}}

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#41 From Dave Copeland Rolling Your Own Dispatch Table Works great with the new Hash and lambda syntax operations = { number: ->(n) { n.to_i }, unary_op: ->(op, n) { n.send("#{op}@") }, binary_op: ->(op, l, r) { l.send(op, r) } } stack = [ ] loop do puts stack.map.with_index { |n, i| "#{i}: #{n}" } print ">> " line = $stdin.gets or break type = case line when %r{\A[-+*/]\Z} then :binary_op when %r{\An\Z} then :unary_op else :number end op = operations[type] stack << op[line.strip.tr('n', '-'), *stack.pop(op.arity - 1)] end

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#42 From Josh Susser Or Just Use Ruby to Dispatch This can be faster than a case statement and calling a lambda class Input; def initialize(input) @input = input end end class Number < Input; def calculate() @input.to_i end end class UnaryOperation < Input; def calculate(n) n.send("#@input@") end end class BinaryOperation < Input; def calculate(l, r) l.send(@input, r) end end stack = [ ] loop do puts stack.map.with_index { |n, i| "#{i}: #{n}" } print ">> " line = $stdin.gets or break type = case line when %r{\A[-+*/]\Z} then BinaryOperation when %r{\An\Z} then UnaryOperation else Number end op = type.new(line.strip.tr('n', '-')) stack << op.calculate(*stack.pop(op.method(:calculate).arity)) end

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#43 From Michael Foley Fetching Data This one method packs so many tricks is hard not to love it params = {var: 42} p params.fetch(:var) p params.fetch(:missing, 42) p params.fetch(:missing) { 40 + 2 } params.fetch(:missing) 42 42 42 /…/fetching_data.rb:8:in `fetch': key not found: :missing (KeyError) ! from /…/fetching_data.rb:8:in `'

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#44 From Jacob Tjørnholm Indexing Into a String by Regex I use this more often than the match operator str = "Price $24.95" p str[/\$\d+(?:\.\d+)?/] p str[/\$(\d+)(?:\.\d+)?/, 1] p str[/\$(?\d+)(?:\.\d+)?/, :dollars]

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#46 From Jacob Tjørnholm You Can Even Assign by Regex I don’t tend to use this version str = "$24.95 per seat" str[/\$\d+(?:\.\d+)/] = "$9.99" puts str str[/\$\d+(?:\.\d+)(\b)/, 1] = " USD" puts str

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#45 Finding the Last Match Work from the right instead of the left expression = "40 + 2 = 42" p expression[expression.rindex(/\d+/)..-1] p expression[expression.rindex(/\b\d+/)..-1]

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#45 Finding the Last Match Work from the right instead of the left expression = "40 + 2 = 42" p expression[expression.rindex(/\d+/)..-1] p expression[expression.rindex(/\b\d+/)..-1]

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#45 Finding the Last Match Work from the right instead of the left expression = "40 + 2 = 42" p expression[expression.rindex(/\d+/)..-1] p expression[expression.rindex(/\b\d+/)..-1] "2" "42"

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#47 From Benjamin Fleischer Chew Through Binary Data These methods are also useful on old “ﬁxed width” data ﬁles width, height = ARGF.read(24).unpack("@16N2") puts " Width: #{width} pixels" puts "Height: #{height} pixels"

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Iterators

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#48 From Benjamin Fleischer Iterating in Lockstep This can walk through two or more collections at once letters = "a".."d" numbers = 1..3 letters.zip(numbers) do |letter, number| p(letter: letter, number: number) end {:letter=>"a", :number=>1} {:letter=>"b", :number=>2} {:letter=>"c", :number=>3} {:letter=>"d", :number=>nil}

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#49 From Piotr Szotkowski Partition Your Data This iterator has been in Ruby a long time now, but I seldom see it used Person = Struct.new(:name, :gender) people = [ Person.new("James", :male), Person.new("Dana", :female), Person.new("Summer", :female) ] males, females = people.partition { |person| person.gender == :male } puts "Males:", males.map { |male| " #{male.name}" } puts "Females:", females.map { |female| " #{female.name}" }

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#50 From Piotr Szotkowski Take Data in Chunks A newer iterator for us to exploit headings = [ "1.1 Compiler Tricks", "1.2 Syntax", "1.3 Data Structures", "1.4 Iterators", "2.1 Core Ruby", "2.2 The Standard Library", "2.3 Tools", "2.4 Black Magic" ] headings.chunk { |heading| heading[/\A\d+/] } .each do |chapter, headings| puts "Chapter #{chapter}:" puts headings.map { |heading| " #{heading}" } end

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#51 map() + flatten() = flat_map() This can be a handy shortcut for working with nested collections require "pp" chess_squares = ("A".."H").flat_map { |column| (1..8).map { |row| "#{column}#{row}" } } pp chess_squares ["A1", "A2", "A3", "A4", "A5", "A6", "A7", "A8", "B1", "B2", "B3", "B4", "B5", "B6", "B7", "B8", "C1", …]

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#52 Replace Ugly inject() Calls This iterator was added to kill a bad yet common usage of inject() # instead of: (1..3).inject({ }) { |hash, n| hash[n] = true; hash } object = (1..3).each_with_object({ }) do |n, hash| hash[n] = true end p object

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#53 Take a Little Off the Top Pull or skip from the beginning of a list numbers = 1..10 p numbers.take(3) p numbers.drop(7) p numbers.take_while { |n| n <= 5 } p numbers.drop_while { |n| n <= 5 }

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#53 Take a Little Off the Top Pull or skip from the beginning of a list numbers = 1..10 p numbers.take(3) p numbers.drop(7) p numbers.take_while { |n| n <= 5 } p numbers.drop_while { |n| n <= 5 }

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#53 Take a Little Off the Top Pull or skip from the beginning of a list numbers = 1..10 p numbers.take(3) p numbers.drop(7) p numbers.take_while { |n| n <= 5 } p numbers.drop_while { |n| n <= 5 }

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#53 Take a Little Off the Top Pull or skip from the beginning of a list numbers = 1..10 p numbers.take(3) p numbers.drop(7) p numbers.take_while { |n| n <= 5 } p numbers.drop_while { |n| n <= 5 }

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#53 Take a Little Off the Top Pull or skip from the beginning of a list numbers = 1..10 p numbers.take(3) p numbers.drop(7) p numbers.take_while { |n| n <= 5 } p numbers.drop_while { |n| n <= 5 } [1, 2, 3] [8, 9, 10] [1, 2, 3, 4, 5] [6, 7, 8, 9, 10]

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#54 Manual Iteration You can step through the new Enumerator objects by hand row = %w[odd even].cycle puts "" ("A".."E").each do |letter| puts %Q{ #{letter}} end puts ""

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#54 Manual Iteration You can step through the new Enumerator objects by hand row = %w[odd even].cycle puts "" ("A".."E").each do |letter| puts %Q{ #{letter}} end puts ""

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#54 Manual Iteration You can step through the new Enumerator objects by hand row = %w[odd even].cycle puts "" ("A".."E").each do |letter| puts %Q{ #{letter}} end puts ""

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#54 Manual Iteration You can step through the new Enumerator objects by hand row = %w[odd even].cycle puts "" ("A".."E").each do |letter| puts %Q{ #{letter}} end puts "" A B C D E

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#55 A Smarter loop() Or get some help from loop() animals = %w[cat bat rat] enum = animals.to_enum 3.times do enum.next end enum.next rescue puts "Error raised: #{$!.class}" enum.rewind loop do puts "Processing #{enum.next}..." end

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#56 From David Brady Chaining Iterators Enumerators also allow for the chaining of iteration p ("a".."z").each_cons(3) .map(&:join) .select { |letters| letters =~ /[aeiouy]/ }

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#56 From David Brady Chaining Iterators Enumerators also allow for the chaining of iteration p ("a".."z").each_cons(3) .map(&:join) .select { |letters| letters =~ /[aeiouy]/ }

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#56 From David Brady Chaining Iterators Enumerators also allow for the chaining of iteration p ("a".."z").each_cons(3) .map(&:join) .select { |letters| letters =~ /[aeiouy]/ } ["abc", "cde", "def", "efg", "ghi", "hij", "ijk", …]

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#57 Add an Index to Any Iterator Enumerator supports this special method just for chaining votes = { "Josh" => %w[SBPP POODR GOOS], "Avdi" => %w[POODR SBPP GOOS], "James" => %w[POODR GOOS SBPP], "David" => %w[GOOS SBPP POODR], "Chuck" => %w[GOOS POODR SBPP] } tally = Hash.new(0) votes.values.each do |personal_selections| personal_selections.each_with_object(tally).with_index do |(vote, totals), i| totals[vote] += personal_selections.size - i end end p tally

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Intermission

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Why Do This? ✤ We trade in the currency of ideas ✤ A bad plan is better than no plan ✤ It’s good to have an appreciation for how rich Ruby is, as a language

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I Don’t Have Time for This!

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Core Ruby

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#58 From Benjamin Fleischer Programmatically Build Classes This allows your code to construct what is needed def build_class(parent, extra_methods = { }) Class.new(parent) do extra_methods.each do |name, result| body = result.is_a?(Proc) ? result : -> { result } define_method(name, &body) end end end Thingy = build_class(Object, value: 42, dynamic: -> { :called }) thingy = Thingy.new p thingy.value p thingy.dynamic

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#59 From Benjamin Fleischer Programmatically Build Modules Modules can also be constructed by code def build_module(extra_methods = { }) Module.new do extra_methods.each do |name, result| body = result.is_a?(Proc) ? result : -> { result } define_method(name, &body) end end end Mixin = build_module(value: 42, dynamic: -> { :called }) thingy = Object.new.extend(Mixin) p thingy.value p thingy.dynamic

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#60 From Benjamin Fleischer Inherit From an Expression Programmatically build parent classes def Value(*fields) Class.new do define_method(:initialize) do |*args| fail ArgumentError, "wrong argument count" unless args.size == fields.size fields.zip(args) do |field, arg| instance_variable_set("@#{field}", arg) end end fields.each do |field| define_method(field) { instance_variable_get("@#{field}") } end end end class Name < Value(:first, :last) def full "#{first} #{last}" end end james = Name.new("James", "Gray") puts james.full

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#61 Mix-in an Expression Module inclusion works the same way def LimitedUse(limit) Module.new do define_singleton_method(:included) do |parent| count = 0 parent.public_instance_methods.each do |method| define_method(method) do |*args| fail "Over use limit" if (count += 1) > limit super(*args) end end end end end class ShortLived include LimitedUse(3) end limited = ShortLived.new puts Array.new(3) { limited.to_s } limited.to_s

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#62 From Avdi Grimm Subclass Module It’s possible to create modules with state class LimitedUse < Module def initialize(limit) @limit = limit super() do define_singleton_method(:included) do |parent| count = 0 parent.public_instance_methods.each do |method| define_method(method) do |*args| fail "Over use limit" if (count += 1) > limit super(*args) end end end end end def to_s; "LimitedUse.new(#{@limit})" end end class ShortLived; include LimitedUse.new(3) end p ShortLived.ancestors limited = ShortLived.new puts Array.new(3) { limited.to_s } limited.to_s

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#63 From Steve Klabnik Empty Types You don’t need a full declaration to deﬁne a class or module module MyNamespace module Errors # instead of: class MyNamespaceError < RuntimeError; end MyNamespaceError = Class.new(RuntimeError) WhateverError = Class.new(MyNamespaceError) end end p MyNamespace::Errors::WhateverError.ancestors

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#63 From Steve Klabnik Empty Types You don’t need a full declaration to deﬁne a class or module [MyNamespace::Errors::WhateverError, MyNamespace::Errors::MyNamespaceError, RuntimeError, StandardError, Exception, Object, Kernel, BasicObject] module MyNamespace module Errors # instead of: class MyNamespaceError < RuntimeError; end MyNamespaceError = Class.new(RuntimeError) WhateverError = Class.new(MyNamespaceError) end end p MyNamespace::Errors::WhateverError.ancestors

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#64 From Chris Hunt Don’t Inherit From Struct Struct takes a block # instead of: class Name < Struct.new(:first, :last) ... end Name = Struct.new(:first, :last) do def full "#{first} #{last}" end end james = Name.new("James", "Gray") puts james.full

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#65 Struct Without the Assignment Subclasses of Struct can be placed under that namespace # instead of: class Name < Struct.new(:first, :last) ... end Struct.new("Name", :first, :last) do def full "#{first} #{last}" end end james = Struct::Name.new("James", "Gray") puts james.full

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#66 From Mike Burns Be a Good method_missing() User Fix respond_to?() and method() for your method_missing() usage class Greeter GREETING_REGEX = /\Aaloha_\w+\z/ def method_missing(method, *args, &block) if method =~ GREETING_REGEX "Aloha #{method.to_s.split("_")[1..-1].map(&:capitalize).join(" ")}" else super end end def respond_to_missing?(method, include_private = false) method =~ GREETING_REGEX end end greeter = Greeter.new p greeter.respond_to?(:aloha_james_gray) puts greeter.method(:aloha_james_gray).call

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#67 instance_eval() In Disguise This trick is faster than the real thing class Whatever def self.peek_inside(&block) define_method(:peek, &block) method = instance_method(:peek) remove_method(:peek) method end def initialize(secret) @secret = secret end end magic_key = Whatever.peek_inside { @secret } meaning = Whatever.new(42) other = Whatever.new(:other) p magic_key.bind(meaning).call p magic_key.bind(other).call

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#68 From Benjamin Fleischer Iterating Over Each Object Remember, we’re talking about MRI here ObjectSpace.each_object do |object| puts object if object.is_a? String end

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#68 From Benjamin Fleischer Iterating Over Each Object Remember, we’re talking about MRI here ObjectSpace.each_object do |object| puts object if object.is_a? String end

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#68 From Benjamin Fleischer Iterating Over Each Object Remember, we’re talking about MRI here ObjectSpace.each_object do |object| puts object if object.is_a? String end .ext CONFIG["PREP"] = "miniruby$(EXEEXT)" EXTOUT no LIBRUBY_RELATIVE ARCHFILE EXECUTABLE_EXTS nodoc …

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#69 From Benjamin Fleischer Iterating Over Specific Types Focus in on speciﬁc objects ObjectSpace.each_object(String) do |object| puts object end

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#69 From Benjamin Fleischer Iterating Over Specific Types Focus in on speciﬁc objects ObjectSpace.each_object(String) do |object| puts object end

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#69 From Benjamin Fleischer Iterating Over Specific Types Focus in on speciﬁc objects .ext CONFIG["PREP"] = "miniruby$(EXEEXT)" EXTOUT no LIBRUBY_RELATIVE ARCHFILE EXECUTABLE_EXTS nodoc … ObjectSpace.each_object(String) do |object| puts object end

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#70 Benjamin Fleischer Count All Objects You don’t need to iterate if you just want counts require "pp" pp ObjectSpace.count_objects

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#70 Benjamin Fleischer Count All Objects You don’t need to iterate if you just want counts require "pp" pp ObjectSpace.count_objects

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#70 Benjamin Fleischer Count All Objects You don’t need to iterate if you just want counts require "pp" pp ObjectSpace.count_objects {:TOTAL=>17579, :FREE=>98, :T_OBJECT=>9, :T_CLASS=>496, :T_MODULE=>23, :T_FLOAT=>7, :T_STRING=>6466, :T_REGEXP=>28, :T_ARRAY=>1222, :T_HASH=>15, :T_BIGNUM=>6, :T_FILE=>10, :T_DATA=>557, :T_MATCH=>109, :T_COMPLEX=>1, :T_NODE=>8510, :T_ICLASS=>22}

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#71 From Peter Cooper Profile the Garbage Collector This can help ﬁnd memory leaks GC::Profiler.enable 10.times do array = Array.new(1_000_000) { |i| i.to_s } end puts GC::Profiler.result

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#71 From Peter Cooper Profile the Garbage Collector This can help ﬁnd memory leaks GC::Profiler.enable 10.times do array = Array.new(1_000_000) { |i| i.to_s } end puts GC::Profiler.result

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#71 From Peter Cooper Profile the Garbage Collector This can help ﬁnd memory leaks GC::Profiler.enable 10.times do array = Array.new(1_000_000) { |i| i.to_s } end puts GC::Profiler.result

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#71 From Peter Cooper Profile the Garbage Collector This can help ﬁnd memory leaks GC::Profiler.enable 10.times do array = Array.new(1_000_000) { |i| i.to_s } end puts GC::Profiler.result GC 21 invokes. Index Invoke Time(sec) Use Size(byte) Total Size(byte) Total Object GC Time(ms) 1 0.010 305000 703480 17587 0.52899999999999991473 2 0.013 588840 719840 17996 0.30400000000000043654 3 0.016 1258720 1276080 31902 0.50300000000000000266 4 0.022 2256520 2274040 56851 0.77800000000000091305 5 0.032 4055240 4073640 101841 1.40099999999999935696 6 0.050 7292960 7312920 182823 2.63900000000000245493 7 0.084 13114280 13137080 328427 4.41699999999999004530 8 0.144 23595920 23623840 590596 7.70400000000001661249 9 0.253 2466120 42486920 1062173 1.61999999999995480948 10 0.410 30496440 42486920 1062173 13.21600000000000463274 11 0.423 30496480 30544120 763603 10.43900000000003203127 12 0.568 14909960 54936880 1373422 7.15099999999990743049 13 0.770 11018240 54936880 1373422 3.72700000000003583978 14 0.932 40182760 46773240 1169331 22.61799999999991683808 15 1.169 40182800 80229440 2005736 26.77799999999997027089 16 1.398 40182840 80229440 2005736 27.82100000000009742962 17 1.628 40182840 80229440 2005736 27.38399999999985112709 18 1.858 40182840 80229440 2005736 27.53000000000005442757 19 2.089 40182840 80229440 2005736 27.83699999999988961008 20 2.322 40182760 80229440 2005736 27.59699999999964958874

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#72 From David Brady Tapping Into a Call Chain Also used to mutate without affecting the return value puts "sssssssssssemaj".sub(/\A(\w)\1+/, '\1') .reverse .capitalize

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#72 From David Brady Tapping Into a Call Chain Also used to mutate without affecting the return value puts "sssssssssssemaj".sub(/\A(\w)\1+/, '\1') .reverse .capitalize James

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#72 From David Brady Tapping Into a Call Chain Also used to mutate without affecting the return value puts "sssssssssssemaj".sub(/\A(\w)\1+/, '\1') .tap { |str| p str.size } .reverse .capitalize

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#72 From David Brady Tapping Into a Call Chain Also used to mutate without affecting the return value puts "sssssssssssemaj".sub(/\A(\w)\1+/, '\1') .tap { |str| p str.size } .reverse .capitalize

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#72 From David Brady Tapping Into a Call Chain Also used to mutate without affecting the return value puts "sssssssssssemaj".sub(/\A(\w)\1+/, '\1') .tap { |str| p str.size } .reverse .capitalize 5 James

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#73 Sneaking in a p() Without tap() In Ruby 1.9, p() returns its argument puts p("sssssssssssemaj".sub(/\A(\w)\1+/, '\1')).reverse.capitalize

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#73 Sneaking in a p() Without tap() In Ruby 1.9, p() returns its argument puts p("sssssssssssemaj".sub(/\A(\w)\1+/, '\1')).reverse.capitalize

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#73 Sneaking in a p() Without tap() In Ruby 1.9, p() returns its argument puts p("sssssssssssemaj".sub(/\A(\w)\1+/, '\1')).reverse.capitalize "semaj" James

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#74 Bubbling Up Thread Errors This can be quite helpful when debugging threaded code Thread.abort_on_exception = true Thread.new do fail "Oops, we can't continue" end loop do sleep end

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#74 Bubbling Up Thread Errors This can be quite helpful when debugging threaded code Thread.abort_on_exception = true Thread.new do fail "Oops, we can't continue" end loop do sleep end

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#74 Bubbling Up Thread Errors This can be quite helpful when debugging threaded code Thread.abort_on_exception = true Thread.new do fail "Oops, we can't continue" end loop do sleep end /…/bubbling_up_thread_errors.rb:4:in `block in ': Oops, we can't continue (RuntimeError)

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#75 The $DEBUG Flag Turn your debugging code on and off as needed def var @var || 40 end if $DEBUG puts "var is %p" % var end p var + 2

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#75 The $DEBUG Flag Turn your debugging code on and off as needed def var @var || 40 end if $DEBUG puts "var is %p" % var end p var + 2

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#75 The $DEBUG Flag Turn your debugging code on and off as needed def var @var || 40 end if $DEBUG puts "var is %p" % var end p var + 2 $ ruby the_debug_flag.rb 42 $ ruby -d the_debug_flag.rb Exception `LoadError' at /…/rubygems.rb:1264 - cannot load such file -- rubygems/defaults/operating_system Exception `LoadError' at /…/rubygems.rb:1273 - cannot load such file -- rubygems/defaults/ruby the_debug_flag.rb:2: warning: instance variable @var not initialized var is 40 the_debug_flag.rb:2: warning: instance variable @var not initialized 42

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#76 Two Tests in One This works on any Comparable object p 2.between?(1, 10) p "cat".between?("bat", "rat")

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#76 Two Tests in One This works on any Comparable object p 2.between?(1, 10) p "cat".between?("bat", "rat")

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#76 Two Tests in One This works on any Comparable object p 2.between?(1, 10) p "cat".between?("bat", "rat") true false

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#77 From Benjamin Fleischer Line-by-line Reading foreach() = open() + each() File.foreach(__FILE__) do |line| p line end

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#77 From Benjamin Fleischer Line-by-line Reading foreach() = open() + each() File.foreach(__FILE__) do |line| p line end

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#77 From Benjamin Fleischer Line-by-line Reading foreach() = open() + each() File.foreach(__FILE__) do |line| p line end "File.foreach(__FILE__) do |line|\n" " p line\n" "end\n"

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#78 The Write-a-file Shortcut You can even dump some data without a call to open() File.write("output.txt", "one\ntwo\nthree\n") puts File.read("output.txt") puts File.write("output.txt", "one and a half\ntwo\n", 4) puts File.read("output.txt") puts File.write("output.txt", "one\ntwo\nthree\n") puts File.read("output.txt")

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#79 Daemonize Your Process I often see Ruby code roll their own, but it’s built-in now Process.daemon loop do sleep end

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#79 Daemonize Your Process I often see Ruby code roll their own, but it’s built-in now Process.daemon loop do sleep end

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#79 Daemonize Your Process I often see Ruby code roll their own, but it’s built-in now Process.daemon loop do sleep end $ ruby daemonize_your_process.rb $ ps auxww | grep daemonize james 27071 … grep daemonize james 27044 … ruby daemonize_your_process.rb james 26564 … emacs daemonize_your_process.rb $ kill 27044 $ ps auxww | grep daemonize james 26564 … emacs daemonize_your_process.rb james 27153 … grep daemonize

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#80 Process Launching on Steroids If you only learn one way to launch a process, let it be spawn() pid = spawn( {"SOME_VAR" => "42"}, # env "./child_process.rb", # the command in: open(__FILE__) ) # options Process.wait(pid) #!/usr/bin/env ruby -w puts "SOME_VAR=%p" % ENV["SOME_VAR"] puts "$stdin.read:", $stdin.read $ ruby process_launching_on_steroids.rb SOME_VAR="42" $stdin.read: pid = spawn( {"SOME_VAR" => "42"}, # env "./child_process.rb", # the command in: open(__FILE__) ) # options Process.wait(pid)

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#81 Seriously, spawn() This sucker has all the features you need spawn({"A_VAR" => "Whatever"}, cmd) # set an environment variable spawn({"A_VAR" => nil}, cmd) # clear an environment variable spawn(env, cmd, unsetenv_others: true) # clear unset environment variables spawn("rm *.txt") # normal shell expansion spawn("rm", "*.txt") # bypass the shell, no expansion spawn(["rm", "sweeper"], "*.txt") # rename command in process list spawn(cmd, pgroup: 0) # change the process group spawn(cmd, rlimit_cpu: Process.getrlimit(:CPU).last) # raise resource limits spawn(cmd, chdir: path) # change working directory spawn(cmd, umask: 0222) # change permissions spawn(cmd, in: io) # redirect IO spawn(cmd, io => [open, args]) spawn(cmd, io => :close) # close an IO spawn(cmd, close_others: true) # close unset IO pid = spawn(cmd); Process.detach(pid) # asynchronous pid = spawn(cmd); Process.wait(pid) # synchronous

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The Standard Library

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#82 Get Random Data Ruby can generate random data for you require "securerandom" p SecureRandom.random_number p SecureRandom.random_number(100) puts p SecureRandom.hex(20) p SecureRandom.base64(20) p SecureRandom.urlsafe_base64(20) p SecureRandom.random_bytes(20) puts p SecureRandom.uuid 0.8337575534446421 50 "5f1edc66708381c18f5527ccc49c0fad7822d5f3" "aoRvYu/V6/MeluooKG+tf4yjyyU=" "WfWpdByTVMdliaymKB_FmqTGgE8" "!d\x94\xE6viS\xCB\xA7\xDB\x84\xCF\x8EY\xCBI\x9F6\xE6\xFD" "5243d395-f317-4394-aa5d-762005d1fe7a"

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#83 From Benjamin Fleischer Read From the Web This is the easiest way to pull something off the Web require "open-uri" open("http://rubyrogues.com/feed/") do |feed| puts feed.read.scan(%r{(\d+\s*RR\b[^<]*)}) end 073 RR APIs 072 RR Entrepreneurship with Amy Hoy 071 RR Zero Downtime Deploys 070 RR What is a Good Starter Project? 069 RR Therapeutic Refactoring with Katrina Owen 068 RR Book Club: Growing Object Oriented Software Guided by Tests 067 RR Gary Bernhardt’s Testing Style 066 RR Rails Bridge with Sarah Mei 065 RR Functional vs Object Oriented Programming with Michael Feathers 064 RR Presenting at Conferences …

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#84 Escape For the Shell This is a great helper when using Ruby as a glue language require "shellwords" p Shellwords.shellwords('one "two" "a longer three"') p Shellwords.shellwords("one 'two' 'a longer three'") p Shellwords.shellwords('"escaped \"quote\" characters"') p Shellwords.shellwords('escaped\ spaces') p Shellwords.shellwords(%Q{'back to'" back quoting"}) p Shellwords.shellescape("two words") p Shellwords.shellescape('"quotes" included') p Shellwords.shelljoin(["two words", '"quotes" included']) ["one", "two", "a longer three"] ["one", "two", "a longer three"] ["escaped \"quote\" characters"] ["escaped spaces"] ["back to back quoting"] "two\\ words" "\\\"quotes\\\"\\ included" "two\\ words \\\"quotes\\\"\\ included"

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#85 From Masatoshi Seki Template Methods Here’s a feature of ERb that I never see used require "erb" class Name def initialize(first, last) @first = first @last = last end attr_reader :first, :last extend ERB::DefMethod def_erb_method("full", "full_name.erb") def_erb_method("last_first", "last_name_first.erb") end james = Name.new("James", "Gray") puts james.full puts james.last_first

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#86 From Piotr Szotkowski Unix Like File Manipulation This library has an excellent interface require "fileutils" FileUtils.mkdir dir, options FileUtils.mkdir_p dir, options FileUtils.ln src, dest, options FileUtils.ln_s src, dest, options FileUtils.cp src, dest, options FileUtils.cp_r src, dest, options FileUtils.mv src, dest, options FileUtils.rm files, options FileUtils.rm_r files, options FileUtils.rm_rf files, options FileUtils.chmod mode, files, options FileUtils.chmod_R mode, files, options FileUtils.chown user, group, files, options FileUtils.chown_R user, group, files, options FileUtils.touch files, options

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#87 From Eric Hodel And You Can Tweak It Get verbose output or try a dry run before you commit to the real thing require "fileutils" module FileSystemWork extend FileUtils # or FileUtils::Verbose, FileUtils::DryRun, ... module_function def do_work touch "file.txt" # or whatever end end FileSystemWork.do_work

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#88 An OO File Interface Pathname combines File, Dir, File::Stat, and more in one pretty interface require "pathname" # build paths dir = Pathname.pwd # or Pathname.new(...) path = dir + __FILE__ # add paths # work with paths puts path.realpath puts path.relative_path_from(dir) puts # use paths to do work path.open do |io| 5.times do puts io.gets end end /Users/james/Desktop/the_standard_library/an_oo_file_interface.rb an_oo_file_interface.rb require "pathname" # build paths dir = Pathname.pwd # or Pathname.new(...) path = dir + __FILE__ # add paths

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#89 From Piotr Szotkowski The World’s Easiest Database It’s multiprocessing safe too require "pstore" db = PStore.new("accounts.pstore") db.transaction do db["james"] = 100.00 db["dana"] = 100.00 end db.transaction do db["dana"] += 200.00 db["james"] -= 200.00 db.abort if db["james"] < 0.0 end db.transaction(true) do puts "James: %p" % db["james"] puts "Dana: %p" % db["dana"] end

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#90 From Piotr Szotkowski Or Use the Drop-in YAML Version Same thing, but human readable require "yaml/store" db = YAML::Store.new("accounts.yml") db.transaction do db["james"] = 100.00 db["dana"] = 100.00 end db.transaction do db["dana"] += 200.00 db["james"] -= 200.00 db.abort if db["james"] < 0.0 end db.transaction(true) do puts "James: %p" % db["james"] puts "Dana: %p" % db["dana"] end

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#91 From Piotr Szotkowski A More Complete Set Array is nice, but this is safer and more full-featured require "set" animals = Set.new animals << "cat" animals.add("bat") p animals.add?("rat") p animals.add?("rat") p animals p animals.member?("tiger") p animals.subset?(Set["bat", "cat"]) p animals.superset?(%w[lions tigers bears].to_set) ordered = SortedSet.new (1..10).to_a.shuffle.each do |n| ordered << n end p ordered

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Tools

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#92 From Benjamin Fleischer Mini Ruby Programs The command-line switches -n, -p, -i, and -e can save you a lot of work $ cat data.txt ones twos threes $ ruby -pi.bak -e 'sub(/s\Z/, "")' data.txt $ cat data.txt one two three $ cat data.txt.bak ones twos threes

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#93 The IO-like ARGF This object wraps Unix style ﬁle arguments in an IO interface ARGF.each_line do |line| puts "#{ARGF.lineno}: #{line}" end

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#93 The IO-like ARGF This object wraps Unix style ﬁle arguments in an IO interface ARGF.each_line do |line| puts "#{ARGF.lineno}: #{line}" end

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#93 The IO-like ARGF This object wraps Unix style ﬁle arguments in an IO interface ARGF.each_line do |line| puts "#{ARGF.lineno}: #{line}" end $ ruby the_iolike_argf.rb one.txt two.txt three.txt 1: one 2: two 3: three

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#94 From Greg Brown ARGF Sans the Command-line You can still use the ARGF magic without Ruby setting it up concatenated_files = ARGF.class.new("one.txt", "two.txt", "three.txt") concatenated_files.each_line do |line| puts line end

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#95 From Benjamin Fleischer The “Flip-flop” Operator Obscure, but it can do a lot of work for you $ cat numbers.txt one two three four five six seven eight nine ten $ ruby -ne 'print if /\At/../e\Z/' numbers.txt two three ten

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#96 From Nick Seiger Out of Order Code This Perlish syntax is handy in one-liners $ cat blenders.txt Ninja $99.99 Vitamix $378.95 Blendtec $399.99 $ ruby -ne 'BEGIN { total = 0 }; END { puts "$%.2f" % total }; total += $_[/\$(\d+(?:\.\d+)?)/, 1].to_f' blenders.txt $878.93

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#97 From Michael Foley IRb’s Last Result This really pays off in a Rails console as well >> "semaj".reverse => "james" >> _.capitalize => "James" >> 40 + 2 => 42 >> n = _ => 42 >> n / 2 => 21

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#97 From Michael Foley IRb’s Last Result This really pays off in a Rails console as well >> "semaj".reverse => "james" >> _.capitalize => "James" >> 40 + 2 => 42 >> n = _ => 42 >> n / 2 => 21

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#98 IRb’s “Job” Managment Pry really wasn’t the ﬁrst >> self => main >> irb "james" >> capitalize => "James" >> jobs => #0->irb on main (#: stop) #1->irb#1 on james (#: running) >> fg 0 => # >> self => main >> fg 1 => # >> self => "james" >> exit => # >> self => main >> exit

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#99 Trigger IRb as Needed It’s often handy to be able to drop into an IRb session require "irb" def my_program_context @my_program_context ||= Struct.new(:value).new(40) end trap(:INT) do IRB.start trap(:INT, "EXIT") end loop do puts "Current value: #{my_program_context.value}" sleep 1 end $ ruby trigger_irb_as_needed.rb Current value: 40 Current value: 40 Current value: 40 ^C1.9.3-p194 :001 > my_program_context.value += 2 => 42 1.9.3-p194 :002 > exit Current value: 42 Current value: 42 Current value: 42

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#100 From Peter Cooper Pretty JSON This tool ships with Ruby 1.9 or later $ curl http://twitter.com/statuses/user_timeline/JEG2.json [{"id_str":"253982951187034113","place":null,"retweeted":false,"in_reply_to_sta tus_id_str":null,"in_reply_to_status_id":null,"in_reply_to_screen_name":null,"i n_reply_to_user_id_str":null,"user":{"id":20941662,"profile_image_url":"http:\/ \/a0.twimg.com\/profile_images\/2311650093\/fkgorpzafxmsafxpf6wi_normal.png","p rofile_background_image_url_https":"https:\/\/si0.twimg.com\/images\/themes\/th eme7\/bg.gif","location":"Edmond, OK","profile_use_background_image":true,"prof ile_text_color":"333333","follow_request_sent":false,"default_profile":false,…

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#100 From Peter Cooper Pretty JSON This tool ships with Ruby 1.9 or later $ curl http://twitter.com/statuses/user_timeline/JEG2.json | prettify_json.rb [ { "id_str": "253982951187034113", "place": null, "retweeted": false, "in_reply_to_status_id_str": null, "in_reply_to_status_id": null, "in_reply_to_screen_name": null, "in_reply_to_user_id_str": null, "user": { "id": 20941662, "profile_image_url": "http://…/fkgorpzafxmsafxpf6wi_normal.png", "profile_background_image_url_https": "https://…/bg.gif", "location": "Edmond, OK", "profile_use_background_image": true, "profile_text_color": "333333", "follow_request_sent": false, …

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Black Magic

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#101 Code That Never Crashes! Ruby is so powerful that it can make code run forever #!/usr/bin/env ruby -w at_exit do if $! and not [SystemExit, Interrupt].include? $!.class exec $PROGRAM_NAME end end loop do left, right = Array.new(2) { rand(-10..10) } operator = %w[+ - * /].sample puts "#{left} #{operator} #{right} = #{left.send(operator, right)}" end