Developing complex regular expressions quickly blows my mind. Here are some online regex editors that help you by highlighting matching text and capture groups:

• Ruby:
  • Rubular
• Javascript:
  • RegExr
  • Regular expression visualizer using railroad diagrams

Capistrano 3 is a major rework of the framework and requires several adjustments to your deploy configuration files. The biggest change is that they moved away from their custom DSL and use Rake instead. For connecting with and operating on the servers, they bring a new gem SSHKit which does the heavy lifting. It's SSHKit's DSL that is used anywhere inside the Rake tasks. See #Resources at the bottom for examples.

Step 1: Upgrade guide

For migration from 2 to 3, follow this tutorial: [Capistrano 3 Upgrade Guide](https://semaphorec...

Re-creating a complex ActiveRecord scenario quickly without setting up a full-blown Rails app can come in handy e.g. when trying to replicate a presumed bug in ActiveRecord with a small script.

# Based on http://www.jonathanleighton.com/articles/2011/awesome-active-record-bug-reports/ 

# Run this script with `$ ruby my_script.rb`
require 'sqlite3'
require 'active_record'

# Use `binding.pry` anywhere in this script for easy debugging
require 'pry'

# Connect to an in-memory sqlite3 database
ActiveRecord::Base.establish_connection(
  ad...

TL;DR Under certain circumstances, dynamically defined symbols may break keyword arguments in Ruby 2.2. This was fixed in Ruby 2.2.3 and 2.3.

Specifically, when …

• there is a method with several keyword arguments and a double-splat argument (e.g. def m(foo: 'bar, option: 'will be lost', **further_options))
• there is a dynamically created Symbol (e.g. 'culprit'.to_sym) that is created before the method is parsed
• the method gets called with both the option and a culprit keyword argument

… then the `optio...

It is a common misunderstanding that all [op]=-operators work the same way, but actually they don't.

||= and &&=

Those are special cases, because the assignment will only happen if the first variable passes the check (false or nil for || and true for &&).

a ||= b   # => a || (a = b)
a &&= b   # => a && (a = b)

But still, if reading a has any side effects, they will take place regardless of to what a resolves.

Other [op]=

Assignment will always take place, no matter the value of a.

When using send_file (for example for attachments of any kind), make sure your application knows the correct mime types so that all browsers can handle the files. It is much more convenient for users if they can decide to open a file directly instead of having to save it first.

For Rails >= 3.2

Simply put your mime types in config/initializers/mime_types.rb. send_file will take care of everything else.

For Rails < 3.2

Put your mime types in config/initializers/mime_types.rb. Additionally, tell send_file to use them (for ex...

You can freeze any Ruby object to prevent further modification.

If you freeze an ActiveRecord and try to set an attribute you will an error like this:

can't modify frozen hash

This is because ActiveRecord delegates #freeze to its attributes hash.

You can unfreeze most Ruby objects by creating a shallow copy of the frozen object by calling #dup on it:

user = User.find(3)
user.freeze
unfrozen_user = user.dup

Notes for Rails 2 users
-----------------...

In RSpec you can tag examples or example groups with any tags you like simply by saying

describe ReportCreator, slow: true do
  # ..
end

describe ReportCreator do
  it 'generates reports', slow: true do
    # ...
  end
end

You can then only run examples with these tags.

rspec --tag slow
rspec -t slow

# Using the parallel_tests gem
rake "parallel:spec[,,--tag slow]"

Or you can run all examples except the ones with a certain tag:

rspec --tag ~slow # note the ~
rspec -t ~slow

# Using the parallel_tests gem
r...

If you want to grow a Ruby Array, you might find out about #fill but it is not really what you are looking for. [1]
For arrays of unknown size that you want to grow or shrink to a fixed size, you need to define something yourself. Like the following.

Array.class_eval do

  def in_size(expected_size, fill_with = nil)
    sized = self[0, expected_size]
    sized << fill_with while sized.size < expected_size
    sized
  end

end

Use it like this:

>> [1, 2, 3].in_size(5)
=> [1, 2, 3, nil, nil]

...

Code folding is a very useful feature to me. It gives me a quick overview over a file and keeps me from scolling like a hamster in its wheel.

Keyboard shortcuts:

Collapse/expand current code block

strg -/+

Collapse/expand the whole file

strg ctrl -/+

When diving into Cucumber features or huge Ruby classes, I usually collapse all and the gradually expand what I need.

When using threads, you must make your code thread-safe. This can be done by either locking (mutexes) all data shared between threads, or by only using immutable data structures. Ruby core classes like String or Array are not immutable.

There are several gems providing thread-safe collection classes in Ruby.

concurrent-ruby

The concurrent-ruby gem provides thread-safe versions of Array and Hash:

sa = Concurrent::Array.new # supports standard Array.new forms
sh = Co...

Today I learned that Ruby on Rails has shipped with a built-in slug generator since Rails 2.2:

> "What Up Dog".parameterize
=> "what-up-dog" 

> "foo/bar".parameterize
=> "foo-bar" 

> "äöüß".parameterize
=> "aouss" 

Also see: Normalize characters in Ruby.

Web applications can be used by multiple users at the same time. A typical application server like Passenger has multiple worker processes for a single app. In a distributed deployment setup like we use at makandra you will even have multiple application servers, each with their own worker pool.

This means that your code needs to deal with concurrent data access. The two main tools we use to cope with concurrency are database transactions and distributed locks. These two are not interchangeable. You ca...

File logger

If you need to log to a file you can use Ruby's Logger class:

require 'logger'

log = Logger.new('log/mylog.log')
log.info 'Some information'
log.debug 'Debugging hints'
log.error StandardError.new('Something went wrong')

Logger does a number of things well:

• Message type (info / debug / error) is logged
• Log entries are timestamped
• Writing log output is synchronized between threads
• Logged errors are printed with full backtraces

If you don't like the output format, you can define a custom formatter.

I ha...

Dusen (our search gem) is now capable of excluding words, phrases and qualified fields from search.
E.g. search for

• included -excluded
• "search this" -"not that"
• topic:"Yes" -topic:"No"

This will soon also work in makandra cards!

This is useful to kill processes like ruby my-script.rb:

pkill -f my-script.rb

With great power comes great responsibility.

You can hook into Slack when using Capistrano for deployment. The slackistrano gem does most of the heavy lifting for you. Its default messages are unobtrusive and can be adjusted easily.

When deploying, it posts to a Slack channel like this:

How to integrate

Integrating Slackistrano with Capistrano 3 is fairly simple.

[NOTE "If you are not a Slack...

If you're on Ruby 2.3+ there's a <<~ operator to automatically unindent HEREDOCs:

str = <<~MESSAGE
  Hello Universe!
  This is me.
             Bye!
MESSAGE

If you have an older Ruby, you can use the String#strip_heredoc method from ActiveSupport. See Summarizing heredoc in ruby and rails for an example.

Technically...

See this Railscast.

Basically you can simply write views like index.xlsx.erb:

<?xml version="1.0"?>
<Workbook xmlns="urn:schemas-microsoft-com:office:spreadsheet"
  xmlns:o="urn:schemas-microsoft-com:office:office"
  xmlns:x="urn:schemas-microsoft-com:office:excel"
  xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet"
  xmlns:html="http://www.w3.org/TR/REC-html40">
  <Worksheet ss:Name="Sheet1">
    <Table>
      <Row>
        <Cell><Data ss:Type="String">ID</Data></Ce...

If you want to sort values from an enumerable into two arrays based on whether they match a certain criteria or not, Enumerable#partition can come in handy.

# Enumerable#partition returns two arrays, 
# the first containing the elements of enum 
# for which the block evaluates to true, 
# the second containing the rest.

(1..6).partition { |v| n.even? }  #=> [[2, 4, 6], [1, 3, 5]]

Works well with destructuring assignment, too.

even, odd = (1..6).partition { |n| n.ev...

The linked article explains how to get a database-wide lock without creating table rows:

This article explains how I replaced file-based methods to ensure only one running instance of a program with MySQL’s GET_LOCK function. The result is mutual exclusivity that works in a distributed environment, and it’s dead simple to implement.

Ruby implementation

An implementation as a Rubygem seems to be [with_advisory_lock](https:...

Postgres 9.4 introduces a new column type: jsonb. json and jsonb columns store data differently, so just compare the two when you want to store JSON data and choose the one that matches your use case best.

Rails 4.2 includes support for jsonb columns, too. The article outlines different ways on how to interact with the serialized object.