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Elixir Cookbook

By : Paulo Pereira
Book Image

Elixir Cookbook

By: Paulo Pereira

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Elixir Cookbook
Paulo Pereira
Feb, 2015 | 236 pages
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Table of Contents (16 chapters)
Elixir Cookbook
Elixir Cookbook
Credits
Credits
About the Author
About the Author
About the Reviewers
About the Reviewers
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
Command Line
Command Line
Introduction
Using the terminal to prototype and test ideas
Loading and compiling modules
Getting help and accessing documentation within IEx
Using Erlang from Elixir
Inspecting your system in IEx
Inspecting your system with Observer
Creating a simple application
Managing dependencies
Generating a supervised application
Generating umbrella applications
Managing application configuration
Creating custom Mix tasks
2
Data Types and Structures
Data Types and Structures
Understanding immutability
Adding and subtracting lists
Combining tuples into a list
Creating and manipulating keyword lists
Using pattern matching
Pattern matching an HTTPoison response
Creating a key/value store with a map
Mapping and reducing enumerables
Generating lazy (even infinite) sequences
Streaming a file as a resource
3
Strings and Binaries
Strings and Binaries
Introduction
Joining strings
Splitting strings
Replacing string codepoints with patterns
Slicing strings with ranges
Using regular expressions
Combining operations with the |> operator
Creating a word list
Determining the word frequency in a text
Reading and writing metadata from MP3 files
4
Modules and Functions
Modules and Functions
Introduction
Namespacing modules
Using module attributes as constants
Enforcing behaviors
Documenting modules
Using module directives
Using a module in the scripted mode
Defining functions with default arguments
Using guard clauses and pattern matching in function definitions
5
Processes and Nodes
Processes and Nodes
Introduction
Sending messages between processes
Making code run on all available CPUs
Using tasks to perform multiple concurrent computations
Creating a stateful server process (messages with counters)
Using agents as an abstraction around states
Using an ETS table to share the state
Creating named nodes
Connecting nodes
Executing code in a different node
6
OTP – Open Telecom Platform
OTP – Open Telecom Platform
Introduction
Implementing a GenServer
Expanding our server
Creating a supervisor
Using Observer to inspect supervisors and processes
Handling errors and managing exceptions
Packaging and releasing an OTP application
Deploying applications and updating a running system
7
Cowboy and Phoenix
Cowboy and Phoenix
Introduction
Setting up Cowboy
Serving static files
Implementing a websocket handler
Creating a Phoenix application
Defining routes
Creating a controller
Creating views and templates
Implementing topics
Protecting the Phoenix app with SSL
8
Interactions
Interactions
Introduction
Using Redis and Postgres
Using OS commands from within Elixir
Getting Twitter data
Installation and Further Reading
Installation and Further Reading
Installing Elixir
Installing PostgreSQL
Installing Redis
Some useful links
Index
Index

Reading and writing metadata from MP3 files

In this chapter's introduction, we mentioned the fact that in Elixir, strings are binaries. In this recipe, we will use a binary file (an MP3 file) and apply some of the operations that we previously performed on strings. We will pattern match the MP3 binary file to extract some information—ID3 v2 information—and we will replace a portion of the file—ID3 v1 information—by constructing a new string and concatenating it to the end of the binary file. In the end, we will still have a proper MP3 file that we will be able to play on our favorite music player!

Note

MP3 files have some metadata stored on them in the form of ID3 tags. The first version of the ID3 tag was stored in the last 128 bytes of the file. The new ID3 tag (v2) is stored at the beginning of the file and may have variable length.

Getting ready

To get started, create a new mp3_info.ex file and add the following code:

defmodule Mp3Info do

  @file_name "Divider.mp3"

  def id3_v2_basic_info...
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