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Published May 21, 2019 Updated November 21, 2020
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XDG

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Provides a Ruby implementation of the XDG Base Directory Specification.

💡 If you write a lot of Command Line Interfaces and would like additional syntactic sugar that includes what is found in this gem, make sure to check out the Runcom gem too.

Features

  • Provides a XDG::Environment 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

Requirements

Setup

To install, run:

gem install xdg

Add the following to your Gemfile:

gem "xdg"

Usage

The following describes how to use this XDG implementation.

Overview

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

xdg = XDG::Environment.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.

The computed value, in this case, 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.

The XDG::Environment wraps the following objects which can be used individually if you don’t want to load the entire environment:

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

The cache, config, and data objects share the same API which means you can ask each 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).

Examples

The following are examples of what you would see when playing around with the XDG objects within an IRB console (taken from my own environment):

require "xdg"

# Initialization
environment = XDG::Environment.new
cache = XDG::Cache.new
config = XDG::Config.new
data = XDG::Data.new

# Inspection
environment.inspect # => XDG_CACHE_HOME=/Users/bkuhlmann/.cache XDG_CONFIG_HOME=/Users/bkuhlmann/.config XDG_CONFIG_DIRS=/etc/xdg XDG_DATA_HOME=/Users/bkuhlmann/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share
cache.inspect # => "XDG_CACHE_HOME=/Users/bkuhlmann/.cache"
config.inspect # => "XDG_CONFIG_HOME=/Users/bkuhlmann/.config XDG_CONFIG_DIRS=/etc/xdg"
data.inspect # => "XDG_DATA_HOME=/Users/bkuhlmann/.local/share XDG_DATA_DIRS=/usr/local/share:/usr/share"

# Paths
environment.cache_home # => #<Pathname:/Users/bkuhlmann/.cache>
environment.config_home # => #<Pathname:/Users/bkuhlmann/.config>
environment.config_dirs # => [#<Pathname:/etc/xdg>]
environment.data_home # => #<Pathname:/Users/bkuhlmann/.local/share>
environment.data_dirs # => [#<Pathname:/usr/local/share>, #<Pathname:/usr/share>]

cache.home # => #<Pathname:/Users/bkuhlmann/.cache>
cache.directories # => []
cache.all # => [#<Pathname:/Users/bkuhlmann/.cache>]

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

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

As you can see from above, each XDG object answers back a Pathname which means you have the full Pathname API at your fingertips to build upon the output of these objects as needed.

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

The $XDG_RUNTIME_DIR deserves special mention as 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_*_HOME

  • $XDG_*_DIRS

Each is described in detail below.

$XDG_*_DIRS

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="/example/one/.config:/example/two/.settings:/example/three/.configuration"

Yields the following, colon delimited, array:

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

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

$XDG_*_HOME

These variables take precidence 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="/example/priority"
XDG_CONFIG_DIRS="/example/one/.config:/example/two/.settings"

Yields the following, colon delimited, array:

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

Due to XDG_CONFIG_HOME taking precidence over the XDG_CONFIG_DIRS, the path with the highest priority in this example is: "/example/priority".

Variable Priority

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

  1. $XDG_*_HOME - Will be used if defined. Otherwise, falls back to specification default.

  2. $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/bkuhlmann/xdg.git
cd xdg
bin/setup

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

bin/console

Tests

To test, run:

bundle exec rake

Versioning

Read Semantic Versioning for details. Briefly, it means:

  • Major (X.y.z) - Incremented for any backwards incompatible public API changes.

  • Minor (x.Y.z) - Incremented for new, backwards compatible, public API enhancements/fixes.

  • Patch (x.y.Z) - Incremented for small, backwards compatible, bug fixes.

Code of Conduct

Read Code of Conduct for details.

Contributions

Read Contributions for details.

License

Read License for details.

History

Read Changes for details.

Credits

Engineered by Brooke Kuhlmann.