Single File Ruby Programs

Welcome!

The Lost Art of Single File Ruby Programs

A loose collection of Ruby fun facts and examples to organize your code in a single file.

Let’s have some fun with Ruby!

Code & tests in one file

Ruby Magic Constants

There is $0.

Contains the name of the file containing the Ruby script being executed.

Source: Pre-defined variables and constants

The source file

def greet(name)
  "Hello #{name}!"
end

# this will only run if the script was the main
# not load'd or require'd
if __FILE__ == $0
  require "test/unit/assertions"
  include Test::Unit::Assertions

  assert_equal 'Hello Ruby', greet('Ruby'), "greet function should return 'Hello Ruby!'"
end

When called directly

$ ruby code_and_test.rb
 greet function should return 'Hello Ruby!'. (Test::Unit::AssertionFailedError)
<"Hello Ruby"> expected but was
<"Hello Ruby!">.

diff:
- Hello Ruby
+ Hello Ruby!
?

When required

require './code_and_test.rb'

puts greet "Christian"

$ ruby code_and_test_usage.rb
Hello Christian!

You may know this from Python

def hello():
    print("Hello world, this script was called!")

if __name__ == '__main__':
    hello()

Source: Python Define Unit Test Classes Together with Code

A webserver in one file?

My life before Ruby

Before Ruby, my favorite web framework was CodeIgniter.

Security first: One index.html file in EVERY folder.

Sinatra 0.6

sudo gem install sinatra

require "rubygems"
require "sinatra"

get '/' do
 "Hello World"
end

Awesome!!!

ruby myapp.rb

Templates: Uncool way

“You can do this too but it’s not as cool” - Sinatra Readme

template :index do
  '%div.title Hello World!'
end

Templates

As documented in the README.rdoc this was the cool way to do it.

get '/' do
  haml :index
end

use_in_file_templates!

__END__

@@ layout
X
= yield
X

@@ index
%div.title Hello world!!!!!

A little Ruby history

Ruby is a better Perl

Why the name ‘Ruby’?

Influenced by Perl, Matz wanted to use a jewel name for his new language, so he named Ruby after a colleague’s birthstone.

Source: The Ruby Language FAQ

Perl’s legacy

Ruby took a lot of things from Pearl.

Today we will learn about:

Keywords
Command line flags

Let’s start with Perldata

Perl has two special literals:

__END__ - Indicates the logical end of the script before the actual end of file. Any following text is ignored.
__DATA__ - A filehandle that points to everything that comes after __END__.

Source: perldata - perldoc.perl.org

The `END` and `DATA` keywords

Denotes the end of the regular source code section of a program file. Lines below __END__ will not be executed.

Those lines will be available via the special filehandle DATA

Source: Class: Object

Simple Example

DATA.each_line do |line|
  puts line
end

__END__
Cats
Dogs
Mice

ERB template and code in one file

require 'erb'

time = Time.now
renderer = ERB.new(DATA.read)
puts renderer.result()

__END__
The current time is <%= time %>.

Explained: Sinatra Style Multiple Templates in File

get '/' do
  haml :index
end

use_in_file_templates!

__END__

@@ layout
X
= yield
X

@@ index
%div.title Hello world!!!!!

File.read(caller.first.split(":").first).split("__END__", 2).last

Source: Mixing code and data in Ruby

PSA: PHP can do it as well

// open self
$fp = fopen(__FILE__, 'rb');
// seek file pointer to data
//__COMPILER_HALT_OFFSET__ will return
//the point after __halt_compiler();
fseek($fp, __COMPILER_HALT_OFFSET__);
// and output it
$unpacked = gzinflate(stream_get_contents($fp));
__halt_compiler();
//now here... all the binary gzdeflate already items!!!

Source: PHP: __halt_compiler - Manual Example: __halt_compiler(), make install files for PHP smaller

Bundler inline

Fun fact: You don’t need a Gemfile to use bundler!

Useful for scripts in your /utils folder that you only use once a year.

Source: How to use Bundler in a single-file Ruby script

Inline HTTParty

require 'bundler/inline'

gemfile do
  gem 'httparty'
end

puts HTTParty.get('https://www.boredapi.com/api/activity')

Inline Minitest

require 'bundler/inline'

gemfile do
  gem 'minitest', require: false
end

require 'minitest/autorun'

class MyTest < Minitest::Test
  def test_should_be_true
    assert_equal true, true
  end
end

Advanced Example: Download iCal to org

Install Dependencies
Do stuff (download calendar events)
Render to ERb template

Source: ical_to_org.rb

`BEGIN` and `END` Keywords

Yes, this is taken from Perl as well.

Definition

BEGIN defines a block that is run before any other code in the current file. It is typically used in one-liners with ruby -e.

Similarly END defines a block that is run after any other code.

Source: Documentation for Ruby 2.2.0

Example

END { puts 3 }
BEGIN { puts 1 }
puts 2

ruby begin.rb
1
2
3

Introducing LRuby

Logging Ruby - The Ruby alias for the forgetful scripter Logging Ruby!

Only Feature: No more scrolling through your terminal… Logs the output of a script to the script itself!

Let’s try this out

cat log_results/hello_world.rb

ruby log_results/hello_world.rb

Introducing: LRuby

lruby log_results/hello_world.rb

cat log_results/hello_world.rb

How does it work?

which lruby

Let’s check out the source of LRuby lruby.rb

The Garbage Flag

Aaaaand back to Perl!

Perlrun

perl -x

Leading garbage will be discarded until the first line that starts with #! and contains the string “perl”.

Source: perlrun - perldoc.perl.org

But… Why?

Tells Perl that the program is embedded in a larger chunk of unrelated text, such as in a mail message.

And in Ruby..

ruby -x

Tells Ruby that the script is embedded in a message. Leading garbage will be discarded until the first that starts with “#!” and contains string “ruby”.

Source: Ruby Docs Command line Options

Example

Hello dear friend,
this is a mail message. Please execute it with your ruby interpreter.

Thanks,
a random stranger
#! hahaha this is ruby now
puts "Hello World"

ruby -x email.eml

A self-animating GIF

This is not an animated gif, but a gif that animates itself.

Let’s talk about GIFs

A GIF file consists of blocks

Example

Terminator Byte

The trailer block indicates when you’ve reached the end of the file. It is always a byte with a value of 3B.

Source: What’s In A GIF

Soooo now we know that..

GIFs are nice
GIFs always end with the same terminator byte
Ruby is nice
Ruby can start with a defined start line
Nice.

A self-animating GIF

This is not an animated gif, but a gif that animates itself.

One file
Upper half is a GIF
Lower half is Ruby code
File rewrites itself!
Profit!

Source Code

Let’s check out the together!

LIVE DEMO!

while 1; do cd /users/fabrik42/desktop/single-file-ruby-programs/rbgif; time ruby -x ./rbgif.gif; sleep 0.1; done

One more thing…

#!/bin/sh

echo This is bash
i=12
echo $i

perl - $i <<'__HERE__'
my $i = shift;
print "This is perl\n";
print ++$i . "\n";
__HERE__

echo This is bash again
echo $i

Source: perl script inside a shell script

Perlmonks.org 2000 Testimonials

“Ain’t that fun?” - dchetlin
“It’s strange and terrible and I’m not sure how to get something out of the perl part, but this sort of works” - eg
“This, on the other hand is just … just .. well, I don’t know. Not right. Not even wrong. It just is.” - Blue

Summary

Ruby is fun!