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Installing Ruby 2.3 or below on Ubuntu 17 and above

From Ubuntu 17, rbenv fails to install Ruby below 2.4 because of a mismatching OpenSSL dependency: it needs libssl1.0-dev for the installation process, but recent Ubuntus come with libssl-dev.

From the linked StackOverflow comment:

As far as I know (and tested), Ruby versions < 2.4 requires libssl1.0, while >2.4 libssl1.1+. The two libssl packages conflict with each other, so you can't have both of them, so I had to juggle the libs in order to install the required ruby version. To make things even funnier (or more complicated),…

Linked content

How to inspect the HTML of an email in Thunderbird

Inspecting the source of an email does not always reveal the plain HTML source, but some encoded byte mess. In order to inspect the HTML anyways, you can use a little trick:

While composing a message, select all (Ctrl + A), then navigate to Insert > HTML on the message window.

If you need to inspect a received message, hit "Reply" to turn it into composition mode.

Linked contentRepeats

How to send HTTP requests using cURL

  • Reading a URL via GET:

    curl http://example.com/
    
  • Defining any HTTP method (like POST or PUT):

    curl http://example.com/users/1 -XPUT
    
  • Sending data with a request:

    curl http://example.com/users -d"first_name=Bruce&last_name=Wayne"
    

    If you use -d and do not set an HTTP request method it automatically defaults to POST.

  • Performing basic authentication:

    curl http://user:password@example.com/users/1
    
  • All together now:

    curl http://user:password@example.com/users/1 -XPUT -d"screen_name=batman"
    

Deal with certain travis CI failures

Travis changed their default distribution from Ubuntu 14.04 (trusty) to 16.04 (precise). This might break your test setup for new builds.

You can solve this issue by freezing your test distribution in the .travis.yml to Ubuntu 14.04 until you have the time to solve all the issues you will have in 16.04:


dist: trusty

Error details

Here are few indicators that you ran into this issue:

Connection to the PostgreSQL database does not work anymore

Your travis-ci builds might have started failing on the usual

```
psql -c…

Repeats

Documenting your Rails project's Node.js version in .nvmrc

Not all versions of Node.js are compatible with each other. Also npm packages may require a minimum or maximum version of Node.js. We use nvm on our development PCs so we can operate multiple versions of Node.js in parallel.

To make sure that all developers use a compatible version of Node.js, your Rails project should declare the required Node.js in a file called .nvmrc.

When a .nvmrc exists, developers can cd in your project directory and activate…

Yarn: How to recognize that you are using a different node version than your colleagues

The issue in this card can occur if the node_modules directory is checked into your Git repository. We usually recommend to exclude node_modules from version control.

In any case you should document which version of node to use in your project in a .nvmrc file.


I saw a strange behaviour after we introduced webpack in one of our projects and finally found out the reason: The person who committed the files used a node version that is older than mine.

Every time I wanted to run my rai…

Linked contentDeprecated

Execution of shell code in Ruby scripts

Deprecated ways to execute shell code in Ruby

This is just a reference for legacy code. For new code, always use capture3.

%x{ } or backticks – quick and easy

Returns the standard output of running the given command in a subshell. This is an alias for `…`, and you can use string interpolation.

Example:

name = 'ls'
result = `which #{name}`

It does not escape anything you inject in the string.

If you want to find out if the call was …

Linked contentDeprecated

How to install npm packages globally without sudo on Linux

All quoted.

  1. Set up a package root in your homedir to hold the Node "global" packages:

    $ NPM_PACKAGES="$HOME/.npm-packages"
    $ mkdir -p "$NPM_PACKAGES"
    
  2. Set NPM to use this directory for its global package installs:

    $ echo "prefix = $NPM_PACKAGES" >> ~/.npmrc
    
  3. Configure your PATH and MANPATH to see commands in your $NPM_PACKAGES prefix by adding the following to your .bashrc:

    ```
    # NPM packages in homedir
    NPM_PACKAGES="$HOME/.npm-packages"

    Tell our environment about user-ins…

How to: Migrate from CoffeeScript to ES6

It is quite easy to migrate from CoffeeScript to ES6. You can use decaffeinate to convert your CoffeeScript source to modern JavaScript.

Installation

  • Install the NPM module globally yarn global add decaffeinate
  • Add the following line to your ~/.bashrc to export the Yarn binaries in your Bash
export PATH="$PATH:$(yarn global bin)"
  • Run decaffeinate some.coffee to get the converted modern JavaScript file.

Notes

  • decaffeinate will add some [suggestions](https://gith…

How to test Autoprefixer and CSSnext in PostCSS

PostCSS is a tool for transforming styles with JS plugins. In Webpacker you can configure the plugins and their settings via the postcss.config.js file.

module.exports = {
  plugins: [
    require('postcss-import'),
    require('postcss-flexbugs-fixes'),
    require('postcss-preset-env')({
      autoprefixer: {
        flexbox: 'no-2009'
      },
      stage: 3
    })
  ]
}

Note: Stage 3 means you can use all CSS features that are listed as "This idea is becoming part of the web". Do not use …

Repeats

When reading model columns during class definition, you must handle a missing/empty database

When doing some meta-programming magic and you want to do something for all attributes of a class, you may need to access connection or some of its methods (e.g. columns) during class definition.

While everything will be fine while you are working on a project that is in active development, the application will fail to boot when the database is missing or has no tables. This means that Raketasks like db:create or db:migrate fail on a freshly cloned project.

The reason is your environment.rb which is loaded for Raketasks and calls…

Migration from the Asset Pipeline to Webpacker

This is a short overview of things that are required to upgrade a project from the Asset Pipeline to Webpacker. Expect this upgrade to take a few days even the diff is quite small afterwards.

Preparations

1. Find all libraries that are bundled with the asset pipeline. You can check the application.js and the application.css for require and import statements. The source of a library is most often a gem or a vendor directory.
2. Find an working example for each library in the application and write it down.
3. Find out the ver…

Repeats

How to search through logs on staging or production environments

We generally use multiple application servers (at least two) and you have to search on all of them if you don't know which one handled the request you are looking for.

Rails application logs usually live in /var/www/<project-environment-name>/shared/log.
Web server logs usually live in /var/www/<project-environment-name>/log.

Searching through single logs with grep / zgrep

You can use grep in this directory to only search the latest logs or zgrep to also search older (already zipped) logs. zgrep is used just like grep a…

How to fix parallel_tests with Redis on powerful machines

When you have a powerful machine with many CPU cores, you might run into an error like

ERR DB index is out of range (Redis::CommandError)

This is because Redis defaults to at most 16 databases (0 to 15) and running tests in parallel might exceed that (your tests might run on databases 1..n or 2..(n+1)).

You can increase that limit:

  1. Get number of CPUs of your machine.

    nproc --all
    
  2. Open up Redis configuration file.

    sudo vim /etc/redis/redis.conf
    
  3. Find databases row and increase it, e.g. set to CPU cou…

How to fix: Session hash does not get updated when using "merge!"

tl;dr: Do not use merge! for session hashes. Use update instead.

Outline

Let's assume you're modifying the Rails session. For simplicity, let's also assume your session is empty when you start (same effect when there is data):

# In our example, we're in a Rack middleware
request = Rack::Request.new(env)
request.session.merge! :hello => 'Universe'
request.session
=> {}

Wat?

Even worse: When you inspect your request.session like above (e.g. in a debugger shell, o…

Repeats

Running external commands with Open3

There are various ways to run external commands from within Ruby, but the most powerful ones are Open3.capture3 and Open3.popen3. Since those can do almost everything you would possibly need in a clean way, I prefer to simply always use them.

Behind the scenes, Open3 actually just uses Ruby's spawn command, but gives you a much better API.

Open3.capture3

Basic usage is

```ruby
require 'open3'

stdout_str, error_str, status = Open3.capture3('/some/binary', 'with', 'some', 'args')
if status.success?…

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 - see below for a list of changes you will probably need
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.
6) Boot the application in different environements to spot further issues, e…

Repeats

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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