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How to start Terminator with split screens and custom commands running

Starting Terminator with split screens is quite simple: Just store a layout and start Terminator with the --layout <your layout> option.

However, if you want to run custom commands in your terminals, you need to do some work to keep these terminals from closing after a command exits. You accomplish this by tweaking bash to run a command before actually starting.

Pimp your .bashrc

Add this to the end of .bashrc:

# hack to keep a bash open when starting it with a command
[[ $startup_cmd ]] && { declare +x $startup_cmd; eval...
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RSpec 3 allows chaining multiple expectations

When you are using lambdas in RSpec to assert certain changes of a call, you know this syntax:

expect { playlist.destroy }.to change { Playlist.count }.by(-1)

While you can define multiple assertions through multiple specs, you may not want to do so, e.g. for performance or for the sake of mental overhead.

RSpec allows chaining expectations simply by using and.

expect { playlist.destroy }
  .to change { Playlist.count }.by(-1)
  .and change { Video.count }.by(0)

The above example will call playlist.destroy only...

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Cheat Sheet for the modern DOM API

See the attached link for a useful overview of modern (and classic) DOM API methods, like matches, contains, append, cssText, etc.

You will still need to look up some documentation, e.g. on how to modify a ClassList, but it's still better than browsing interfaces and superclasses of Element on MDN without knowing what to look for.

When coming from jQuery, also see the card on JavaScript without jQuery. This card includes a link to [You Don't Need jQuery](https://github.com/nefe/You-Dont-Need-jQuery/blob/maste...

How to extract a Ruby gem

The rubygems binary gem allows to extract a local gem with gem unpack GEMNAME. For more details see the official documentation.


This was useful for compliance checks, when it was necessary to check the license of the C-files in nokogiri.

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Spreewald development steps

Our gem spreewald supports a few helpers for development. In case you notice errors in your Cucumber tests, you might want to use one of them to better understand the underlying background of the failure. The following content is also part of the spreewald's README, but is duplicated to this card to allow repeating.

Then console

Pauses test execution and opens an IRB shell with current cont...

CarrierWave: When your uploader generates filenames dynamically, use model.save! instead of uploader.recreate_versions!

If your Carrierwave uploader dynamically generates the filename (e.g. by incorporating a user's name), you must call model.save! after recreating versions.

uploader.recreate_versions! does not update the model with the stored filename.

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Simple database lock for MySQL

Note: For PostgreSQL you should use advisory locks. For MySQL we still recommend the solution in this card.


If you need to synchronize multiple rails processes, you need some shared resource that can be used as a mutex. One option is to simply use your existing (MySQL) database.

The attached code provides a database-based model level mutex for MySQL. You use it by simply calling

Lock.acquire('string to synchronize on') do
  # non-t...
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Debugging AJAX requests with better_errors

better_errors is an awesome gem for enhanced error pages in development, featuring a live-REPL for some light debugging.

To debug the exception you got on an AJAX-Request, visit /__better_errors on your app's root path (e.g. http://localhost:3000/__better_errors). It shows the error page for the last exception that occurred, even when it has been triggered by an AJAX request.

CSS: How to force background images to scale to the container, ignoring aspect ratio

You can scale background images in CSS to the container size using background-size (Demo).

Commonly, we use contain or cover because we want to preserve the image's aspect ratio.
If you do not want to do that, simply provide scaling values for X and Y:

background-size: 100% 100%

(a simple 100% would mean 100% auto and respect the image's aspect ratio)

SVGs with a viewBox will force their aspect ratio

The above may not work for you when ...

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Updated: Cucumber: Testing file downloads with Selenium

Added two more methods:

Method 3: Use a request spec

Only test that the download link's [href] attribute points to a particular route.

Then test that route with a request spec. Or, if the uploaded file lives in public/, test that the linked file exists.

Method 4: Test without Selenium

If you can get away with it, run that one test with Rack::Test instead of Selenium. With a Rack::Test driver Capybara allows some access to the response headers via page.driver.response.headers.

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Deprecated: BigDecimal arithmetic in Ruby

Nowadays multiplying or adding BigDecimal with Float results in BigDecimal. This is the case for at least Ruby >= 2.3.

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How Rails chooses error pages (404, 500, ...) for exceptions

When your controller action raises an unhandled exception, Rails will look at the exception's class and choose an appropriate HTTP status code and error page for the response.

For instance, an ActiveRecord::RecordNotFound will cause Rails to render a red "The page you were looking for doesn't exist" with a status code of "404" (not found).

The mapping from exception classes to error types is a hash in Rails.configuration.action_dispatch.rescue_responses. The...

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Heads up: RSpec's diffs may not tell the truth

RSpec provides a nice diff when certain matchers fail.

Here is an example where this diff is helpful while comparing two hashes:

{a:1}.should match(a:1, b:2)

Failure/Error: {a:1}.should match(a:1, b:2)
  expected {:a=>1} to match {:a=>1, :b=>2}
  Diff:
  @@ -1,3 +1,2 @@
   :a => 1,
  -:b => 2,

Unfortunately, this diff is not as clever as it would need to. RSpec's instance_of matchers will look like errors in the diff (even if they are not), and time objects that differ only in milliseconds won't appear in the ...

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Ruby: What extend and include do

All Rubyists should be familiar with the common definitions for include and extend. You include a module to add instance methods to a class and extend to add class methods. Unfortunately, this common definition isn’t entirely accurate. It fails to explain why we use instance.extend(Module) to add methods to an instance. Shouldn’t it be instance.include(Module)? To figure this out we’re going to start by discussing where methods are stored.

  • include: Adds methods from the provided Module to the object
  • extend: Calls include on the single...

Setting SASS variables as value for CSS custom properties

When using custom properties in your stylesheets, you may want to set a specific property value to an existing variable in your SASS environment. A pratical example would be a list of color variables that you've defined in colors.sass and that you would like to refer to in your stylesheets. However, simply assigning a variable will not work:

$my-great-blue: blue

:root
  --my-color: $my-great-blue

.sky
  background-color: var(--my-color)

The property value will not be valid and if you open the browser's inspection window, yo...

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makandra_rubocop 6.2.0. released

In case you include the spec helper from makandra_rubocop (require 'makandra_rubocop/support/rubocop_spec') in the spec/rubocop_spec.rb, you might want to upgrade makandra_rubocop to get better error messages on failures and in projects with deprecation warnings from e.g. parser.

6.2.0 - 2021-06-20

Compatible changes

  • Use the format simple output, and not progress.
  • Also output stdout if stderr is present. Otherwise warnings like
    whitequark/parser will block the actual offenses message to be skipped.
    Originally we thoug...
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Updated: Customize your Bash prompt

Added a bash prompt with an indicator for git stashes.

Headless Chrome: Changing the Accept-Language header is not possible

It seems like changing the HTTP_ACCEPT_LANGUAGE is not possible for a headless chrome.

  • On Ubuntu the headless Chrome derives the Accept-Language from the operation system
  • Adding the option options.add_argument('--lang=de') to the Capybara::Selenium::Driver has no effect
  • Adding the preference options.add_preference('intl.accept_languages', 'de') to the Capybara::Selenium::Driver has only effects if the --headless option is skipped (see bug ticket #775911)
  • Cha...
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