HOWTOs for Ruby on Rails and JavaScript

grosser/rspec-instafail

Gem to show failing specs instantly.
Unlike the --fail-fast option it doesn't abort abort on the first failure, but keeps running other examples after print out the failure.

I haven't tried it with parallel_tests.

github.com

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The developer console can do more than you think!

You can do so much more than console.log(...)! See the attached link for a great breakdown of what the developer console can give you.

Some of my favorites:

console.log takes many arguments

E.g. console.log("Current string:", string, "Current number:", 12)

Your output can have hyperlinks to Javascript objects

E.g. console.log("Check out the current %o, it's great", location)

[Di...

developer.mozilla.org

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Installing Adobe Reader on Ubuntu

Adobe no longer supports their PDF reader on Linux and the official page does not offer it for download. \
However, some files may not display properly on Ubuntu's default PDF reader Evince or PDF forms may not work as expected. Hence, you may still need to use it.

Here is how to install the Adobe Reader (acroread) if you need to:

Download the .deb archive from the Adobe servers (yes, it's still there):

cd /tmp && wget http://ardownload.adobe.com/pub/adobe/reader/unix/9.x/9.5.5/enu/AdbeRdr9.5.5-1_i386linux_enu.deb

I...

askubuntu.com

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LibreOffice Writer prints text frames as black areas

To fix this:

Right-click on the frame
Select Frame...
Open Background
Set As to "Color"
Set the background color to "No fill"

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Bootstrap: How to avoid printing link URLs

By default, Twitter Bootstrap's print styles include printing links.

/* Bootstrap's way of printing URLs */
@media print {
  a[href]:after {
    content: " (" attr(href) ")";
  }
}

If you want to turn that off, you can do

/* Don't print link hrefs */
@media print {
  a[href]:after {
    content: none
  }
}

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Fixing tlmgr cannot setup TLPDB

tlmgr is the TeX Live Manager and responsible for the TeX installation on your (Linux) machine.

If you're getting the message:

(running on Debian, switching to user mode!)
cannot setup TLPDB in /home/dominik/texmf at /usr/bin/tlmgr line 5336.

... tlmgr has not been initialized. Run this to initialize it:

tlmgr init-usertree

Then, you may set e.g. a global paper size standard: tlmgr paper a4.

tex.stackexchange.com

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How to repair a corrupt PDF

If you have issues with PDFs, fix them like this: pdftk <corrupted_file>.pdf output <fixed_file>.pdf

Background

I had an issue where an included PDF would not show up in a document created with xelatex. This is the relevant line of LaTeX code:

  \AddToShipoutPicture*{ \includegraphics[width=21cm]{/home/dominik/code/ihero/public/system/stationery/original/stationery.pdf} }

The included PDF is a stationery for invoices which users can upload themselves. It did work until someone updated their stationery with a nearly-iden...

blog.idrsolutions.com

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How to install the `xelatex` binary on Ubuntu 14.04

Just install the texlive-xetex package:

sudo apt-get install texlive-xetex

Running integration tests without texlive-xetex will produce an error during xelatex execution:

RTeX::Document::ExecutableNotFoundError

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When Sass-generated stylesheets print a Encoding::CompatibilityError

We upgraded a Rails 2 application to Rails 3.2 and Ruby 2.1, changed the mysql adapter from mysql to mysql2, but did not activitate the asset pipeline. Instead we used Sass the old-school way (stylesheets in public/sass/*.sass) and relied on stylesheet_link_tag to activate the Sass compiler.

Now all Sass-generated stylesheets inserted the following text into body:before:

Encoding::CompatibilityError: incompatible character encodings: UTF-8 and ASCII-8BIT

I could get rid of this by removing all generated .css files in `...

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pdfkit/wkhtmltopdf: When a header is invisible

If you're using the :header_html option in PDFKit (or the corresponding --header-html option in wkhtmltopdf), and the header remains invisible, you need to add this to your header HTML:

<!doctype html>

The same applies to footers via footer_html

I'm sorry.

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Linux: Running a program with a different locale than your default

When your system is not running on English, you may sometimes want to run some applications and not use your system locale.
Use cases are scripts that parse output, or just using the (possibly) more common English labels or error messages. Here is how to do that.

I will use the date command and print the current weekday, just for the sake of an example.

Changing the locale using environment variables

Most often, setting LC_ALL for your command should be enough. The following was run on a system using a German locale.

$ date +%...

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What we know about PDFKit

What PDFKit is

PDFKit converts a web page to a PDF document. It uses a Webkit engine under the hood.
For you as a web developer this means you can keep using the technology you are familar with and don't need to learn LaTeX. All you need is a pretty print-stylesheet.

How to use it from your Rails application

You can have PDFKit render a website by simply calling PDFKit.new('http://google.com').to_file('google.pdf'). You can then send the...

github.com

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Ruby lets you redefine backticks

This actually works:

class Klass

  def initialize
    `hi world`
  end

  def `(message)
    puts "Called with backticks: #{message}"
  end
  
end

Klass.new # Prints "Called with backticks: hi world"

Hat tip to @jcoglan.

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PSA: Umlauts are not always what they seem to be

When you have a string containing umlauts which don't behave as expected (are not matched with a regexp, can't be found with an SQL query, do not print correctly on LaTeX documents, etc), you may be encountering umlauts which are not actually umlaut characters.

They look, depending on the font, like their "real" umlaut counterpart:

ä ↔ ä
ö ↔ ö
ü ↔ ü

However, they are not the same:

'ä' == 'ä' # false
'ä'.size # 1
'ä'.size # 2

Looking at how those strings are constructed reveals what is going on:

'ä'.unpack('U*...

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Lightweight PDF viewer: MuPDF

MuPDF is a PDF reader that renders very quickly, yet still correctly.

It supports PDF 1.7 and all the fancy shenanigans that evince (Ubuntu's default PDF reader) fails to render properly.

On Ubuntu, MuPDF is available in the Universe sources. Simply install via APT:

sudo apt-get install mupdf

Interaction primarily happens via keyboard, but there is basic mouse support.\
See the manpage for more details on navigating.

One downside: There is no printing support, so if...

mupdf.com

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A Ruby script that installs all gems it is missing

So you want your Ruby script to install missing gems instead of dying? Take this method:

def installing_missing_gems(&block)
  yield
rescue LoadError => e
  gem_name = e.message.split('--').last.strip
  install_command = 'gem install ' + gem_name
  
  # install missing gem
  puts 'Probably missing gem: ' + gem_name
  print 'Auto-install it? [yN] '
  gets.strip =~ /y/i or exit(1)
  system(install_command) or exit(1)
  
  # retry
  Gem.clear_paths
  puts 'Trying again ...'
  require gem_name
  retry
end

Use it like this:

insta...

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About "unexpected '#' after 'DESCENDANT_SELECTOR' (Nokogiri::CSS::SyntaxError)"

The error unexpected 'x' after 'DESCENDANT_SELECTOR' (Nokogiri::CSS::SyntaxError) (where x may be basically any character) occurs when the Nokogiri parser receives an invalid selector like .field_with_errors # or td <strong>.

In Cucumber, the culprit will be an invalid step definition that builds an invalid selector:

# inside some step definition:
field = find_field(label)
page.send(expectation, have_css(".field_with_errors ##{field[:id]}"))

The above raises the mentioned error if field[:id] is nil, i.e. the foun...

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Offtopic: Floppy-disc OS

MenuetOS is an Operating System in development for the PC written entirely in 32/64 bit assembly language. Menuet64 is released under License and Menuet32 under GPL. Menuet supports 32/64 bit x86 assembly programming for smaller, faster and less resource hungry applications.

Fits on a single floppy, boots also from CD and USB drives
Responsive GUI with resolutions up to 1920x1080, 16 million colours
Free-form, transparent and skinnable application windows, drag'n drop
SMP multiprocessor support with currently up to 8 cpus
IDE: E...

menuetos.net

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Rails 2: Refuse response formats application-wide

If you regularly get ActionView::MissingTemplate exceptions, maybe some bot visits your site requesting silly formats like:

http://www.rails-app.com/makandra.html-username-2000 # => Rails tries to retrieve 'makandra' with format 'html-username-2000'

Just restrict accepted format parameters for the whole application like this:

class ApplicationController < ActionController::Base

  before_filter :refuse_silly_formats

  private

  def refuse_silly_formats
    acceptable_formats = %w[html xml pdf]

    if par...

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Linux: How to print PDF files from the command line

Sometimes you may want to print files from the command line, especially when you have lots of them.
You can use lp for that.

To print a single example.pdf file on your default printer, simply say:

lp example.pdf

lp accepts multiple filenames, so to print all PDF files in the current directory:

lp *.pdf

You can specify a printer via the -d switch:

lp -d YOUR_PRINTER_NAME *.pdf

Your printer's name is then one you defined on your system. You can check with your CUPS configuration by visiting `http://localhost:631/...

linux.die.net

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PDF Generation in Rails

A look at Prawn, PDFKit, and Wicked PDF

sitepoint.com

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Bash: Heavy headings for CLI

To print a colored full-width bar on the bash, use this bash script expression:

echo -e '\033[37;44m\nHEADING\033[0m\nLorem ipsum ...'

In Ruby:

  puts "\033[37;44m\n #{text}\033[0m" # blue bar

Notes: -e turns on escape character interpretation for echo. See this card for details on bash formatting.

The line above will print:

Bildschirmfoto_2014-03-08_um_21.24.55.png

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How to load only a subset of a massive MySQL dump

I had a huge MySQL dump that took forever (as in: days) to import, while I actually just wanted to have the full database structure with some data to use on my development machine.

After trying several suggestions on how to speed up slow MySQL dump imports (which did not result in any significant improvement), I chose to import just some rows per table to suffice my needs. Since editing the file was not an option, I used a short Ruby script to manage that.

Here is how:

pv huge.dump | ruby -e 'ARGF.each_line { |l| m = l.match(/^INSERT ...

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Ruby constant lookup: The good, the bad and the ugly

In Ruby, classes and modules are called constants. This card explains how Ruby resolves the meaning of a constant.

The good

E. g. in the following example, Array could mean either Foo::Array or simply Array:

class Foo
  def list
    Array.new
  end
end

What Ruby does here is to see if the name Array makes sense inside of Foo::, and if that fails, resolves it to ::Array (without a namespace).

The bad

This is relevant for old Ruby versions. Ruby 2.5+ removes top-level constant lookup whi...

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