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Published November 3, 2016 Updated February 20, 2024
Runcom Icon



Runcom is a Run Command portmanteau (i.e. run + [com]mand = runcom) which provides common functionality for Command Line Interfaces (CLIs) in which to manage global/local caches, configurations, data, and/or state. This is done by leveraging the XDG Base Directory Specification built atop the XDG implementation. In other words, Runcom is an enhanced version of XDG which specializes in dynamic global and local detection.


  • Wraps the XDG implementation which provides access to the following environment variables:







  • Enhances the XDG cache, config, data, and state implementations with dynamic global and local detection.



To install with security, run:

# 💡 Skip this line if you already have the public certificate installed.
gem cert --add <(curl --compressed --location
gem install runcom --trust-policy HighSecurity

To install without security, run:

gem install runcom

You can also add the gem directly to your project:

bundle add runcom

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

require "runcom"


The following describes the enhancements built atop the XDG implementation.


While there isn’t a sole convenience object as found with the XDG gem, you can instantiate each object individually:

cache = "demo/data.json"
config = "demo/configuration.yml"
data = "demo/store.dat"
state = "demo/history.log"

By default, each Runcom object expects a relative file path but you can also use a fully qualified path when constructing a new instance.

Each of the above objects share the same Object API:

  • #initial: Answers the initial path — which can be a relative or absolute path — from which the object was constructed.

  • #namespace: Answers the namespace as a pathname object from which the instance was constructed. The namespace must be unique and identical across the cache, config, data, and state objects since this is what identifies and organizes all files associated with your program.

  • #file_name: Answers the file name from which the object was constructed.

  • #active: Answers first existing file path as computed by $XDG_*_HOME followed by each computed $XDG_*_DIRS path in order defined. Otherwise, nil is answered back when no path exists.

  • #passive: Answers first path as computed by $XDG_*_HOME followed by each computed $XDG_*_DIRS path in order defined which may or may not exist. This behaves like #active but doesn’t care if the path exists. Handy for situations where you’d like the active path but can fallback to creating the global path if otherwise.

  • #global: Answers the first existing or non-existing global path.

  • #local: Answers the first existing or non-existing local path.

  • #all: Answers all paths which is the combined $XDG_*_HOME and $XDG_*_DIRS values in order defined. These paths may or may not exist.

  • #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 following are examples of what you will see when exploring the Runcom objects within an IRB console:

# Initialization

cache = "demo/projects.json"
config = "demo/settings.yml"
data = "demo/"
state = "demo/history.log"

# Paths

cache.initial     # "#<Pathname:demo/projects.json>"
cache.namespace   # "#<Pathname:demo>"
cache.file_name   # "#<Pathname:projects.json>"      # nil
cache.passive     # "#<Pathname:/Users/demo/.cache/demo/projects.json>"      # "#<Pathname:/Users/demo/.cache/demo/projects.json>"
cache.local       # "#<Pathname:/Users/demo/Engineering/OSS/runcom/.cache/demo/projects.json>"
cache.all         # ["#<Pathname:/Users/demo/Engineering/OSS/runcom/.cache/demo/projects.json>", "#<Pathname:/Users/demo/.cache/demo/projects.json>"]

config.initial    # "#<Pathname:demo/settings.yml>"
config.namespace  # "#<Pathname:demo>"
config.file_name  # "#<Pathname:settings.yml>"     # nil
config.passive    # "#<Pathname:/Users/demo/.config/demo/settings.yml>"     # "#<Pathname:/Users/demo/.config/demo/settings.yml>"
config.local      # "#<Pathname:/Users/demo/Engineering/OSS/runcom/.config/demo/settings.yml>"
config.all        # ["#<Pathname:/Users/demo/Engineering/OSS/runcom/.config/demo/settings.yml>", "#<Pathname:/Users/demo/.config/demo/settings.yml>", "#<Pathname:/etc/xdg/demo/settings.yml>"]

data.initial      # "#<Pathname:demo/>"
data.namespace    # "#<Pathname:demo>"
data.file_name    # "#<>"       # nil
data.passive      # "#<Pathname:/Users/demo/.local/share/demo/>"       # "#<Pathname:/Users/demo/.local/share/demo/>"
data.local        # "#<Pathname:/Users/demo/Engineering/OSS/runcom/.local/share/demo/>"
data.all          # ["#<Pathname:/Users/demo/Engineering/OSS/runcom/.local/share/demo/>", "#<Pathname:/Users/demo/.local/share/demo/>", "#<Pathname:/usr/local/share/demo/>", "#<Pathname:/usr/share/demo/>"]

state.initial     # "#<Pathname:demo/history.log>"
state.namespace   # "#<Pathname:demo>"
state.file_name   # "#<Pathname:history.log>"      # nil
state.passive     # "#<Pathname:/Users/demo/.local/state/demo/history.log>"      # "#<Pathname:/Users/demo/.local/state/demo/history.log>"
state.local       # "#<Pathname:/Users/demo/Engineering/OSS/runcom/.local/state/demo/history.log>"
state.all         # ["#<Pathname:/Users/demo/Engineering/OSS/runcom/.local/state/demo/history.log>", "#<Pathname:/Users/demo/.local/state/demo/history.log>"]

# Casts (explicit and implicit)

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

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

# Inspection

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

Variable Priority

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

  1. Local Configuration: If a $XDG_*_HOME or $XDG_*_DIRS path relative to the current working directory is detected, it will take precedence over the global configuration. This is the same behavior as found in Git where the local .git/config takes precedence over the global $HOME/.gitconfig.

  2. Global Configuration: When a local configuration isn’t found, the global configuration is used as defined by the XDG Base Directory Specification.

Building Blocks

While XDG and Runcom are powerful in their own right, a great building block you can add on top of this gem is the Etcher gem which loads, transforms, validates, and produces structured data from raw Runcom information. For more sophisticated applications, this synergetic coupling of XDG + Runcom + Etcher makes for nicely designed architectures.


Examples of gems built atop this gem are:

  • Rubysmith: A command line interface for smithing Ruby projects.

  • Gemsmith: A command line interface for smithing new Ruby gems.

  • Hanamismith: A command line interface for smithing Hanami projects.

  • Git Lint: Enforces consistent Git commits.

  • Milestoner: A command line interface for releasing Git repository milestones.

  • Pennyworth: A command line interface that enhances and extends Alfred with Ruby support.

  • Pragmater: A command line interface for managing/formatting source file pragma comments.

  • Sublime Text Kit: A command line interface for managing Sublime Text metadata.

  • Tocer: A command line interface for generating Markdown table of contents.


To contribute, run:

git clone
cd runcom

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


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.



To test, run: