When attempting to update RubyGems, depending on updates your previously performed, you might run into an error

ERROR:  While executing gem ... (TypeError)
can't convert nil into String

Fix this by running

gem uninstall rubygems-update -a -x

We're usually running Ubuntu LTS versions. Sometimes newer hardware requires packages from more recent Ubuntu releases that only come with 6 months of support. If there is really no other way, it's possible to install packages from later Ubuntu releases

Caution: Pay really close attention to what you're doing. Depending on the package, this process may require upgrading a lot of dependencies, possibly breaking the system! You really should not do this unless you've carefully calculated the impact on your system

Preparation

First,...

If you open a pop-up window [1] in your Selenium tests and you want to close it, you can do this:

# Find our target window
handle = page.driver.find_window("My window title")

# Close it
page.driver.browser.switch_to.window(handle)
page.driver.browser.close

# Have the Selenium driver point to another window
last_handle = page.driver.browser.window_handles.last
page.driver.browser.switch_to.window(last_handle)

Mind these:

• find_window returns a window handle, which is something like `"{485fa8bd-fa99-...

Ruby allows multiple assignment:

a, b, c = o

In order to prove multiple values from a single object, Ruby calls #to_a on the object:

o = String.new('O')
def o.to_a
  [1,2,3]
end

a, b, c = o # Implicit call to #to_a here
a # => 1
b # => 2
c # => 3

Hence, if you want your class to support multiple assignment, make sure to define a #to_a method.

If you use awesome and make a Slack call, you'll constantly have an overlay window pop up taking over half of your screen.

To fix this, add the following rule to your awful.rules.rules section in your rc.lua:

awful.rules.rules = {
  -- ...
  { rule = { name = "Slack Call Minipanel" }, properties = { floating = true, ontop = true } },
}

Precondition

• You are not using javascript tests
• The file is served from a public folder (not via controller)

Problem description

If you deliver files from a public folder it might be that the Content-Disposition header is not set. That's why the following spreewald step might raise an error:

Then I should get a download with filename "..."

expected: /filename="some.pdf"$/
     got: nil (using =~) (RSpec::Expectations::ExpectationNotMetError)

Solution

One solution...

These steps are now part of Spreewald.

Since Capybara 0.4.1 a within scope will only look at the first element that matches. We find this behavior to be impractical, but it is by design.

In order to perform a test or action in all matching elements, do not use within but prefer the attached "inside any" Cucumber steps like these:

When I follow "Foo" inside any "table"
Then I should see "Bar" inside any "li"

If you are using PDFKit / wkhtmltopdf, you might as well want to use custom fonts in your stylesheets. Usually this should not be a problem, but at times they include misleading Meta-information that leads to a strange error in the PDF.

The setup

• The designer gave you two fonts named something like BrandonText-Regular and BrandonText-Bold. (With flawed Meta-information)
• You have a HTML string to be rendered by PDFKit
• For demonstration purposes, this strin...

Let's say you have a folder images and want to to move all files in there to a new subfolder public.

cd images
mkdir public
mv !(public) public

The !(public) excludes the new subfolder itself from being moved.

The linked article shows how to exploit websites that include unsanitized user input in their CSS.

Although the article often mentions React and CSS-in-JS libraries, the methods are applicable to any web app that injects user input into style tags or properties.

Also, sanitizing user input for CSS injection is much harder than sanitizing HTML.

Hack to implement an inverted "night mode" theme with a few lines of CSS.

Colors in images are preserved.

TL;DR: Bundler 2.0 will rename Gemfile to gems.rb and Gemfile.lock to gems.locked (sic).

The old filenames will be supported until the release of Bundler 3.0.

Some more breaking changes here.

You need to set the :inverse_of option manually for relations that have an association to a polymorphic model. Otherwise you will not be able to save a record with a nested polymorphic association.

class Event < ApplicationRecord
  has_many :letters, as: :record
end

class Letter < ApplicationRecord
  belongs_to :record, polymorphic: true
end

event = Event.new.letters.build
event.save! # => ActiveRe...

While the hardware mute button of my Lenovo x230 worked on Ubuntu 14.04 out of the box, it does not on Ubuntu 16.04. It is fairly simple to fix, though.

There is an extensive answer on Ask Ubuntu, but only part of it was required for me. Here is the gist of it.

1. Open a terminal

2. Run acpi_listen and press the mute key. You should see something like this:

   button/f20 F20 00000080 00000000 K
   

   Press Ctrl+C to exit.

3. Run amixer scontrols. You will see multiple lines, one of which sh...

Let's say you have a form that you render a few times but you would like to customize your submit section each time. You can achieve this by rendering your form partial as layout and passing in a block. Your template or partial then serves as the surrounding layout of the block that you pass in. You can then yield back the form to the block and access the form in your block.

-# record/_form.haml

= form_for record do |form|
  -# ...
  .form-actions
    yield(form)
  

In order to make your template record/_form.haml accept a...

FactoryBot allows a :class option to its factory definitions, to set the class to construct. However, this option is not supported for traits.

Most often, you can just define a nested factory instead of a trait, and use the :class option there.

factory :message do
  factory :reply, class: Message::Reply do
    # ...
  end
end

If you need/want to use traits instead (for example, it might make more sense semantically), you can not use a :class on a trait.

In that case, use initialize_with to define the record's constr...

There are several gems that make it easy to read and process xlsx files. Parsing the entire file at once however is error-prone since each cell is transformed to a ruby object - sometimes including thousands of formatted but empty cells.

As of today, I found two promising alternatives that provide a stream-based access to spradsheet rows:

• Roo supports multiple spreadsheet types like ODS or CSV and has a quite large contributor base
• [Creek](https://github.com/pythonicrubyis...

On my Ubuntu MATE machine, switching applications with ALT + TAB was impossible, because it took nearly 2 seconds. The culprit appears to be an "UX improvement" gone bad: MATE renders a live screenshot of each running application inside the application switcher.

Fixing this is simple:

• Open "Window Preferences"
• Either uncheck "Enable software compositing window manager" or check "Disable thumbnails in Alt-Tab"

The linked documentation explains how to get a JSON list of the latest 100 events of a given issue. Simply open this URL while logged in:

https://sentry.io/api/0/issues/<issue id>/events/

If another session is accessing your database you are trying to reset or drop you might have seen the following error:

PG::ObjectInUse: ERROR:  database "foo_development" is being accessed by other users
DETAIL:  There is 1 other session using the database.

This could be the rails server, rubymine and many more. Beside terminating the session connection manually you can also find out the pid and kill the process.

1. rails db
2. SELECT * FROM pg_stat_activity;

datid            | 98359
datname          | foo_developm...

You need to disable "Bluetooth low energy", then follow these core steps:

1. Make sure the headphones are in pairing mode.
2. Pair with System Settings > Bluetooth. On 16.04 I had to choose "proceed without pairing" and enter the PIN "0000"
3. Select & test the headphones in System Settings > Sound. Choose High Fidelity Playback (A2DP Sink).

I also had to install a package with sudo apt-get install pulseaudio-module-bluetooth and load it with pactl load-module module-bluetooth-discover. Put the latter command into ~/.bashrc or you'll...

Here is some JavaScript code that allows you to click the screen and get the clicked element's text contents (or value, in case of inputs).

The approach is simple: we place an overlay so you don't really click the target element. When you click the overlay, we look up the element underneath it and show its text in a browser dialog. You can then copy it from there.

While moving the mouse, the detected element is highlighted.

Here is the one-liner URL that you can store as a bookmark. Place it in your bookmarks bar and click it to activate....

I frequently find myself needing a combination of group_by, count and sort for quick statistics. Here's a method on Enumerable that combines the three:

module Enumerable
  def count_by(&block)
    group_by(&block)
      .transform_values(&:count)
      .sort_by(&:last)
      .to_h
  end
end

Just paste that snippet into a Rails console and use #count_by now!

Usage examples

• Number of email addresses by domain:

> User.all.count_by { |user| user.email.sub /^.*@/, '' }
=> { "sina.cn"=>2, ..., "hotmail.com"=>128...