RubyGems can't find bundle executable although Bundler is installed

I had this error:

> gem install bundler
Successfully installed bundler-2.0.1
1 gem installed

> bundle install
Traceback (most recent call last):
	2: from /home/henning/.rbenv/versions/2.5.1/bin/bundle:23:in `<main>'
	1: from /home/henning/.rbenv/versions/2.5.1/lib/ruby/2.5.0/rubygems.rb:308:in `activate_bin_path'
/home/henning/.rbenv/versions/2.5.1/lib/ruby/2.5.0/rubygems.rb:289:in `find_spec_for_exe': can't find gem bundler (>= 0.a) with executable bundle (Gem::GemNotFoundException)

The cause was that Bundler 2 requires RubyG…

Auto-generating plain-text bodies for HTML e-mails in Rails apps

When building an application that sends e-mails to users, you want to avoid those e-mails from being classified as spam. Most obvious scoring issues will not be relevant to you because you are not a spammer.

However, your application must do one thing by itself: When sending HTML e-mails, you should include a plain-text body or tools like SpamAssassin will apply a significant score penalty. Here is how to do that automatically.

  1. Add premailer-rails to your Gemfile and bundle.
  2. Done! …

Upgrading Ruby from 1.8.7 to 2.3.5

Suggested Workflow

Set the ruby version in .ruby-version to 2.3.5, then perform these steps one by one, fixing errors as they occur:

1) Update gems as listed below, and bundle
2) Boot a Rails console
3) Run Specs with --backtrace option
4) Run Cucumber features (with Geordi's --debug option)
5) When all tests are green, look through your Gemfile and remove as many version constraints as possible

Gem updates

  • Replace ruby-debug with byebug or pry
  • Replace mysql with mysql2, '< 0.3'
  • Remove oniguruma
  • Remove…

Ruby: Reading and writing CSVs

In ruby you can easily read and write CSVs with the standard CSV library class.

On top of this, you can use the gem smarter_csv for reading (not writing) CSVs in a more comfortable way:

  • Keep in mind, that the development of this gem is in an unknown state and the 2.0 release seems to happen never
  • The API will change completely for 2.0, so you might find a bunch of unrelated documentation for 1.2

Here is an example…


Live CSS / view reloading

Next time you have to do more than trivial CSS changes on a project, you probably want to have live CSS reloading, so every time you safe your css, the browser updates automatically. It's pretty easy to set up and will safe you a lot of time in the long run. It will also instantly reload changes to your html views.

Simply follow the instructions below, taken from

Install CSS live reload (only once per project)

  1. Add th…

Cucumber: How to find unused step definitions

Cucumber has an output format that prints step definitions only. You can use this to find unused ones:

  1. Temporarily add require_relative 'env' to the top of the first file in features/support. --dry-run makes Cucumber skip loading env.rb.
  2. Open a really wide terminal window.
  3. bundle exec cucumber --dry-run --format stepdefs | grep -B1 'NOT MATCHED' --no-group-separator | grep features/step_definitions

This will print all unused step definitions from your project – however, the result will include false positives. Step…

How to upgrade Rails: Workflow advice

When upgrading Rails versions – especially major versions – you will run into a lot of unique issues, depending on the exact version, and depending on your app.

However, it is still possible to give some generic advice on how you want to tackle the update in principle.

How many update steps?

Besides the Rails upgrade itself, you might also want to

  • upgrade your other gems
  • upgrade your Ruby versions

First decide in how many steps you want to run the upgrade. I suggest

  • To do a separate step for each major rails versions. So, if…

Exception notifier: How to provide custom data to fail mails

The exception_notification gem supports to provide custom data to e.g. the fail mail within foreground or background jobs.

ExceptionNotifier.notify_exception(_ex_, :data => {:message => "was doing something wrong"})

Still this can be blocked if you have an initializer where you override the default sections and background_sections option. So remember to add the data option to the desired section if required. In case you raise an exception without a data object, the fail…

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Katapult 0.5.0 released

New Features

  • Deployment ready for Opscomplete
  • Copying view and controller templates over to target application during
    basics configuration or via new command katapult templates.
  • "Usage" section in README rewritten: Now describes two usage scenarios.


  • Generating a fixed Gemfile.lock. Run bundle update after code generation to
    update all gems to recent versions.
  • Better deployment with Webpack
  • Navigation only rendered if requested
  • Some minor fixes

How to: Run geordi in a single proccess with parallel test setup

Geordi uses parallel_tests if available for running the test suite. To debug an application it is very unhandy to have multiple processes as your terminal I/O will not work as expected once a breakpoint is hit.

Even parallel_tests support an option to enable a single process run, it is not possible to pass this option through geordi. But you can set the number of processes via ENV variable manually:

PARALLEL_TEST_PROCESSORS=1 bundle exec geordi cucu…


How to examine an unknown Ruby object

When debugging your application, you will come across objects created by some gem or framework. You don't have the source code at hand, still need to inspect this object. Here are some tools to do so:

Relevant methods

@object.methods - Object.instance_methods returns a list of methods excluding methods inherited from Object. This makes the methods list drastically more relevant. You can also try subtracting other base classes like ActiveRecord::Base.methods etc.

Filtering method list

@object.methods.grep /keyword/ comes…

Rbenv: How to remove a gem installed from a Github source

Normally you can list all gems of the current ruby version with gem list, which also includes the gems of you Gemfile. These can be uninstalled with gem uninstall gemname.

List and uninstall a gem installed via Bundler from Github

This does not work for gems installed directly from Github. They do not appear in gem list.

Show all gems installed via Github by bundler:

ls ~/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/bundler/

Remove a gem installed via Github by Bundler:

rm -rf ~/.rbenv/versions/2.4.1/lib/ruby/gems/2….

Linked contentRepeats

How to let passenger restart after deployment with capistrano

Phusion Passenger changed the way how it gets restarted several times. Through the project's history, these all were valid:

  • touch tmp/restart.txt
  • sudo passenger-config restart-app /path/to/app
  • passenger-config restart-app /path/to/app

You should not need to know which one to use. Instead, the capistrano-passenger gem will choose the appropriate restart mechanism automatically based on your installed the passenger version.


  1. Add to your Gemfile:

    gem 'capistr...

An incomplete guide to migrate a Rails application from paperclip to carrierwave

In this example we assume that not only the storage gem changes but also the file structure on disc.

A general approach

Part A: Create a commit which includes a script that allows you to copy the existing file to the new file structure.

Part B: Create a commit which removes all paperclip logic and replace it with the same code you used in the first commit

Part A

Here are some implementation details you might want to reuse:

  • Use the existing models to read the files from
  • Use your own carrierwave models to write t…

Debugging cucumber feature with javascript + firefox vnc

TL;DR Debugging problems with javascript errors in cucumber tests is sometimes easier in the browser. Run the test, stop at the problematic point (with Then pause from Spreewald 1.7+) and open VNC for Firefox.



Geordi: How to rerun failed features

Cucumber will save a file tmp/parallel_cucumber_failures.log will the filenames and line number of the failed scenarios after a full test run.

Normally you can say cucumber -p rerun (rerun is a profile defined by default in config/cucumber.yml) to rerun all failed scenarios. Unfortunately this does not work with geordi yet.

Here is a list of possible workarounds:

geordi firefox bundle exec cucumber -p rerun
cat tmp/parallel_cucucmber_failures.log | xargs geordi cucumber
geordi cucumber `cat…


Rails < 5: How to get after_commit callbacks fired in tests

If you use transactional_fixtures or the database_cleaner gem with strategy :transaction, after_commit callbacks will not be fired in your tests.

Rails 5

Rails 5 has a fix for this issue and no further action is needed.

Rails 3+

Add the gem test_after_commit to your test group in the Gemfile and you are done. You don't need to change the database strategy to deletion (which might…


Collect all values for a given column in an ActiveRecord scope

The Edge Rider gem allows you to collect an array of values for one field of your ActiveRecord elements:

=> [1, 5, 23, 42]

It also comes with a :distinct option in case you are only interested in unique values:

>> Article.collect_column(:state, distinct: true)
=> ['draft', 'published']

In modern Railses (since 3.2) you can also use ActiveRecord's pluck met…

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