Submit fixes on github
Follow me on twitter

How to map from a range

Subtle syntax difference results in major functional change:

[0..10].map { 1 }  
# => [1]  

(0..10).map { 1 }  
[1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]  

Replace characters with tr

"1337".tr("137", "let")  
# => "leet"  

Reminder that if/else are expressions in ruby:

a = if true  

(ruby, install, 3.2.2, rvm, openssl)

I was having problems installing ruby on a friend’s machine.
Had to use:

rvm install ruby-3.2.2 --with-openssl-dir=$(brew --prefix openssl)  

(ruby repl, irb, insert line in existing function)

Up arrow to previously executed code in irb
Use Opt+Enter to add a new line without executing

(ruby, system, exception, raise if error from shell, default does not raise)

None of these raise by default:

system "exit 1"  
`exit 1`  
%x(exit 1)  

Instead, use:

system "exit 1", exception: true  

(ruby, map, symbol syntax, symbol to proc)

The symbol to proc functionality assumes that the symbol is a member of the
calling instance. To call a pure function, use my_array.map(&method(:my_fn)).
For example:

def add_one(n)  
  return n + 1  

[1,2,3].map &method(:add_one)  

(ruby debug, ruby 3)

Either use:

require "debug"  
:: Add breakpoint in source with `debugger`  

Or add binding.irb in source, no require necessary.
I prefer the former, because stepping (n) and continuing (c) through the source works.

(ruby 3 irb autocomplete, navigate autocomplete popup)

Move down: Tab
Move up: Shift-Tab

(ruby disable irb autocomplete)

Start irb with irb --noautocomplete
or add IRB.conf[:USE_AUTOCOMPLETE] = false to ~/.irbrc

(ruby, erb, howto)

    require "erb"  
    my_variable = "hello world"  
    result = ERB.new(File.read("myfile.txt.erb")).result(binding)  
    File.write("myfile.txt", result)  

(rvm upgrade, rvm update ruby version)

rvm get stable

(rvm set default ruby version)

rvm --default use X.Y.Z

(rvm, ruby, remove rvm)

rvm implode

(rvm, name a version of ruby for local use)

rvm alias create myruby ruby-2.4.1  
rvm use myruby  

(ruby, global vars, cheat sheet)


(ruby gem install dir)

See where bundler finds a specific gem:

bundle show <gemname>  

(ruby koans, assert, testing, education)


(ruby ruby, sexp, lexer, parser, tokenize)


(ruby, find methods defined lower in class tree)

List methods on an instance that are defined outside of Object:

class Object  
    def local_methods  
      (methods - Object.instance_methods).sort  

(ruby, irb, faulty ~/.irbrc, debugging)

To see why ~/.irbrc is not working properly:

ruby ~/.irbrc  

(irb, default configuration)

/private/etc/irbrc holds the default irb config, can be overwritten by creating a ~/.irbrc file.

(ruby, rackup, reload on file system changes)

See the rerun gem

$ rerun --background --no-growl rackup service.ru  

(ruby, pry, irb, autocomplete, source exploration, discovery)

Pry is really sweet.

$ pry  
> cd FileUtils  
> ls  
> show-method mkdir  

(ruby, time, active support, time helpers, number of seconds)

require 'active_support/time'

I added this here:

(irb, source exploration, discovery)

Given a starting value, see what method will give the desired result with what_methods.

require 'what_methods'  
10.what? "10" #=> 10.to_s, 10.inspect  


(ruby, colorize irb prompt, colorize rails console prompt):

require "wirble"  
IRB.CurrentContext.prompt_i = Wirble::Colorize.colorize_string(IRB.CurrentContext.prompt_i, :red)  

(ruby, gems, get location on disk)

gem env

(rvm, which rvm)

After installing rvm, I was surprised that which rvm exited with 1.
rvm is a function that’s sourced into my shell.
Use command -v rvm to see if my shell can find it.
Use bash --debugger -cl "declare -F rvm" to find where the function is defined.
The output will contain the definition file on disk and the source line number.

(ruby, rubygems, load automatically)

Do not add require "rubygems" to code.
Start ruby with ruby -rubygems, or irb with irb -rrubygems, or add this to ~/.bash_profile:

export RUBYOPT="rubygems"  

source: https://tomayko.com/blog/2009/require-rubygems-antipattern

(ruby, regex, dot star, does not match new line)

Here is an interesting difference:

irb> a = "string with \n new line"  
irb> a =~ /(.*)/  
irb> $1  
=> "string with "  

irb> a =~ /([^"]*)/  
irb> $1  
=> "string with \n new line"  

The .* does not match new lines, but negated class does

(ruby, class variables, inheritance works as expected)

class A  
  @greeting = "hello"  
  class << self  
    attr_reader :greeting  

class B < A  
  @greeting = "hola"  

A.greeting # => "hello"  
B.greeting # => "hola"  

(ruby, iterate all error classes at runtime)

ObjectSpace.each_object(Class) do |cls|  
  if cls.ancestors.include? Exception  
    puts cls  

(ruby, irb, find class name in irb)

irb> self.class.constants.select { |c| c =~ /needle/i }  

(ruby, send message, dynamic, dynamic method call)

object.message is the same as object.send(:message)

For example, 5.send :to_s

(ruby, variable in regex)

a = "[0-9]+"  
b = /#{a}/  

(ruby, pad a month string to two digits)

month = 5  
month.to_s.gsub(/^(\d)$/, '0\1')  

(ruby, add N months to current month)

month = ((month - 1 + N ) % 12) + 1  

(ruby, irb, benchmark in irb)

require 'benchmark'  
include Benchmark  

bm(10) do |test|  
    test.report("result 1:") do  
      # test something  
    test.report("result 2:") do  
      # test something else  

(ruby, reference semantics, array, create array of empty arrays)


array = Array.new(2,[])  
array[0][0] = "x"  
# => [["x"], ["x"]]  
# Both subarrays are filled with "x" (it's really one array)  


array = Array.new(2) { [] }  
array[0][0] = "x"  
# => [["x"], []]  

(ruby, instance eval, I thought this was once a good idea)

These accomplish the same thing:

class Test  
  attr_accessor :one, :two, :three  
  def initialize(one, two, three)  
    @one = one  
    @two = two  
    @three = three  


class Test  
    attr_accessor :one, :two, :three  
    def initialize(&block)  
        instance_eval &block  
Test.new {self.one = 1; self.two = 2; self.three = 3}  

(ruby, color, term, escape code, irb)

Loop through escape sequences in IRB to pick a color:

(30..50).each do |x|  
  puts x  
  print "\e[#{x}mTEST\e[0m\n"  

(ruby, is daylight savings in effect?)