XDG

8.2.0

Provides a Ruby implementation of the XDG Base Directory Specification for managing common configurations without polluting your Dotfiles. XDG is great for command line interfaces or any application that needs a common configuration, cache, data, state, or runtime.

💡 If you write a lot of Command Line Interfaces (CLIs) and would like additional behavior built atop this gem, then check out the Runcom gem or the more advanced Sod gem.

Table of Contents

Features

Provides a XDG object that adheres to the XDG Base Directory Specification with access to the following environment settings:
- $XDG_CACHE_HOME
- $XDG_CONFIG_HOME
- $XDG_CONFIG_DIRS
- $XDG_DATA_HOME
- $XDG_DATA_DIRS
- $XDG_STATE_HOME

Requirements

Ruby

Setup

To install with security, run:

# 💡 Skip this line if you already have the public certificate installed.
gem cert --add <(curl --compressed --location https://alchemists.io/gems.pem)
gem install xdg --trust-policy HighSecurity

To install without security, run:

gem install xdg

You can also add the gem directly to your project:

bundle add xdg

Once the gem is installed, you only need to require it:

require "xdg"

Usage

The following describes how to use this implementation.

Objects

To get up and running quickly, use XDG.new as follows:

xdg = XDG.new
xdg.cache_home   # Answers computed `$XDG_CACHE_HOME` value.
xdg.config_home  # Answers computed `$XDG_CONFIG_HOME` value.
xdg.config_dirs  # Answers computed `$XDG_CONFIG_DIRS` value.
xdg.data_home    # Answers computed `$XDG_DATA_HOME` value.
xdg.data_dirs    # Answers computed `$XDG_DATA_DIRS` value.
xdg.state_home   # Answers computed `$XDG_STATE_HOME` value.

Behinds the scenes, use of XDG.new wraps XDG::Environment.new which provides a unified Object API to the following objects:

cache = XDG::Cache.new
config = XDG::Config.new
data = XDG::Data.new
state = XDG::State.new

Generally, use of XDG.new is all you need but knowing you can create a specialized instance of any aspect of the XDG specification can be handy for specific use cases. Additionally, the cache, config, data, and state objects share the same API which means you can send the following messages:

#home: Answers the home directory as computed via the $XDG_*_HOME key.
#directories: Answers an array directories as computed via the $XDG_*_DIRS key.
#all: Answers an array of all directories as computed from the combined $XDG_*HOME and $XDG*DIRS values (with $XDG*_HOME prefixed at the start of the array).
#to_s: Answers an explicit string cast for the current environment.
#to_str: Answers an implicit string cast for the current environment.
#inspect: Answers object inspection complete with object type, object ID, and all environment variables.

The computed value of each method is either the user-defined value of the key or the default value, per specification, when the key is not defined or empty. For more on this, scroll down to the Variable Defaults section to learn more.

Examples

The following are examples of what you will see when exploring the XDG objects within an IRB console:

require "xdg"

# Initialization

xdg = XDG.new
cache = XDG::Cache.new
config = XDG::Config.new
data = XDG::Data.new
state = XDG::State.new

# Paths

xdg.cache_home      # "#<Pathname:/Users/demo/.cache>"
xdg.config_home     # "#<Pathname:/Users/demo/.config>"
xdg.config_dirs     # ["#<Pathname:/etc/xdg>"]
xdg.data_home       # "#<Pathname:/Users/demo/.local/share>"
xdg.data_dirs       # ["#<Pathname:/usr/local/share>", "#<Pathname:/usr/share>"]
xdg.state_home      # "#<Pathname:/Users/demo/.local/state>"

cache.home          # "#<Pathname:/Users/demo/.cache>"
cache.directories   # []
cache.all           # ["#<Pathname:/Users/demo/.cache>"]

config.home         # "#<Pathname:/Users/demo/.config>"
config.directories  # ["#<Pathname:/etc/xdg>"]
config.all          # ["#<Pathname:/Users/demo/.config>", "#<Pathname:/etc/xdg>"]

data.home           # "#<Pathname:/Users/demo/.local/share>"
data.directories    # ["#<Pathname:/usr/local/share>", "#<Pathname:/usr/share>"]
data.all            # ["#<Pathname:/Users/demo/.local/share>", "#<Pathname:/usr/local/share>", "#<Pathname:/usr/share>"]

state.home          # "#<Pathname:/Users/demo/.local/state>"
state.directories   # []
state.all           # ["#<Pathname:/Users/demo/.local/state>"]

# Casts (explicit and implicit)

xdg.to_s            # "XDG_CACHE_HOME=/Users/demo/.cache XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share XDG_STATE_HOME=/Users/demo/.local/state"
cache.to_s          # "XDG_CACHE_HOME=/Users/demo/.cache"
config.to_s         # "XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg"
data.to_s           # "XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share"
state.to_s          # "XDG_STATE_HOME=/Users/demo/.local/state"

xdg.to_str          # "XDG_CACHE_HOME=/Users/demo/.cache XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share XDG_STATE_HOME=/Users/demo/.local/state"
cache.to_str        # "XDG_CACHE_HOME=/Users/demo/.cache"
config.to_str       # "XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg"
data.to_str         # "XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share"
state.to_str        # "XDG_STATE_HOME=/Users/demo/.local/state"

# Inspection

xdg.inspect         # "#<XDG::Environment:2020 XDG_CACHE_HOME=/Users/demo/.cache XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share XDG_STATE_HOME=/Users/demo/.local/state>"
cache.inspect       # "#<XDG::Cache:2040 XDG_CACHE_HOME=/Users/demo/.cache>"
config.inspect      # "#<XDG::Config:2060 XDG_CONFIG_HOME=/Users/demo/.config XDG_CONFIG_DIRS=/etc/xdg>"
data.inspect        # "#<XDG::Data:2080 XDG_DATA_HOME=/Users/demo/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share>"
state.inspect       # "#<XDG::State:2100 XDG_STATE_HOME=/Users/demo/.local/state>"

Variable Defaults

The XDG Base Directory Specification defines environment variables and associated default values when not defined or empty. The following defaults, per specification, are implemented by the XDG objects:

$XDG_CACHE_HOME="$HOME/.cache"
$XDG_CONFIG_HOME="$HOME/.config"
$XDG_CONFIG_DIRS="/etc/xdg"
$XDG_DATA_HOME="$HOME/.local/share"
$XDG_DATA_DIRS="/usr/local/share/:/usr/share/"
$XDG_RUNTIME_DIR
$XDG_STATE_HOME="$HOME/.local/state"

The $XDG_RUNTIME_DIR environment variable deserves special mention because it’s not, currently, implemented as part of this gem because it is more user/environment specific. Here is how the $XDG_RUNTIME_DIR is meant to be used should you choose to use it:

Must reference user-specific non-essential runtime files and other file objects (such as sockets, named pipes, etc.)
Must be owned by the user with only the user having read and write access to it.
Must have a Unix access mode of 0700.
Must be bound to the user when logging in.
Must be removed when the user logs out.
Must be pointed to the same directory when the user logs in more than once.
Must exist from first login to last logout on the system and not removed in between.
Must not allow files in the directory to survive reboot or a full logout/login cycle.
Must keep the directory on the local file system and not shared with any other file systems.
Must keep the directory fully-featured by the standards of the operating system. Specifically, on Unix-like operating systems AF_UNIX sockets, symbolic links, hard links, proper permissions, file locking, sparse files, memory mapping, file change notifications, a reliable hard link count must be supported, and no restrictions on the file name character set should be imposed. Files in this directory may be subjected to periodic clean-up. To ensure files are not removed, they should have their access time timestamp modified at least once every 6 hours of monotonic time or the ‘sticky’ bit should be set on the file.
When not set, applications should fall back to a replacement directory with similar capabilities and print a warning message. Applications should use this directory for communication and synchronization purposes and should not place larger files in it, since it might reside in runtime memory and cannot necessarily be swapped out to disk.

Variable Behavior

The behavior of most XDG environment variables can be lumped into two categories:

$XDG_*_DIRS
$XDG_*_HOME

Each is described in detail below.

Directories

These variables are used to define a colon (:) delimited list of directories. Order is important as the first directory defined will take precedent over the following directory and so forth. For example, here is a situation where the XDG_CONFIG_DIRS key has a custom value:

XDG_CONFIG_DIRS="/demo/one/.config:/demo/two/.settings:/demo/three/.configuration"

The above then yields the following, colon delimited, array:

[
  "/demo/one/.config",
  "/demo/two/.settings",
  "/demo/three/.configuration"
]

In the above example, the "/demo/one/.config" path takes highest priority since it was defined first.

Homes

These variables take precedence over the corresponding $XDG_*DIRS environment variables. Using a modified version of the $XDG*_DIRS example, shown above, we could have the following setup:

XDG_CONFIG_HOME="/demo/priority"
XDG_CONFIG_DIRS="/demo/one/.config:/demo/two/.settings"

The above then yields the following, colon delimited, array:

[
  "/demo/priority",
  "/demo/one/.config",
  "/demo/two/.settings"
]

Due to XDG_CONFIG_HOME taking precedence over the XDG_CONFIG_DIRS, the path with the highest priority is: "/demo/priority".

Variable Priority

Path precedence is determined in the following order (with the first taking highest priority):

$XDG_*_HOME - Will be used if defined. Otherwise, falls back to specification default.
$XDG_*_DIRS - Iterates through directories in order defined (with first taking highest priority). Otherwise, falls back to specification default.

Development

To contribute, run:

git clone https://github.com/demo/xdg
cd xdg
bin/setup

You can also use the IRB console for direct access to all objects:

bin/console

Lastly, there is a bin/demo script which displays default functionality for quick visual reference. This is the same script used to generate the usage examples shown at the top of this document.

bin/demo

Tests

To test, run:

bin/rake

Credits

Built with Gemsmith.
Engineered by Brooke Kuhlmann.

XDG