Imperial

Imperial provides access to the standard directory structure in UNIX and Linux, as defined by the systemd and XDG Base Directory specifications.

Features

• Typesafe representation of standard UNIX directories
• Supports any directory representation through typeclasses
• Resolves environment variables to correctly use user-specified directory locations
• Supports alternative sources of environment variables

Availability

The current latest release of Imperial is 0.4.0.

Getting Started

Standard directory layout

Imperial provides a structure of nested objects inside the Root and Home objects which mirror the standard directory layout on modern UNIX systems, as described in the (XDG Base Directory Specification](https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html). This allows standard directories to be referenced in code without the risk of typos.

Additionally, certain environment variables may be set which change the standard location, particularly within a user's home directory. Imperial will take these into account, according to the specification.

Accessing Directories

Objects have the same names as their corresponding UNIX directory, but by convention begin with a capital letter. Any . prefixes in a directory's name are removed since, of course, . is used in place of / to access a nested object. So /var/lib would be represented by the object, Root.Var.Lib and $HOME/.local/bin would be Home.Local.Bin.

Conversely, Home.Config would normally resolve to $HOME/.config, but if the user has the XDG_CONFIG_HOME environment variable set to something else, it would simply resolve to $XDG_CONFIG_HOME.

The type of each of these objects is BaseLayout, which provides a BaseLayout#apply() method for constructing an instance of a directory type (such as java.io.File or joviality.Directory) representing the directory. Imperial is designed to be compatible with different file and directory representations, but it works automatically with Joviality.

For example, it would be possible to access a myapp configuration directory with,

import joviality.*
val dir: Directory = Home.Config() / t"myapp"

Source of Environment Variables

By default, Imperial will take its environment variables directly from the JVM, since they are globally accessible. But this is not always the correct source, for example in a long-running server which may receive multiple command-line requests from different shells over its lifetime, each with a potentially different set of environment variables.

To cater for this scenario, it's possible to provide an alternative EnvVarProvider instance. This is a single-abstract-method trait which takes a Text value and returns an Option[Text] of the value (returning None if the environment variable is unset).

For example, if the envvars is a Map of values, a new EnvVarProvider may be specified in-scope with,

given EnvVarProvider = envvars.get(_)

Related Projects

The following Scala One libraries are dependencies of Imperial:

No other Scala One libraries are dependents of Imperial.

Status

Imperial is classified as fledgling. Propensive defines the following five stability levels for open-source projects:

• embryonic: for experimental or demonstrative purposes only, without any guarantees of longevity
• fledgling: of proven utility, seeking contributions, but liable to significant redesigns
• maturescent: major design decisions broady settled, seeking probatory adoption and refinement
• dependable: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version 1.0 or later
• adamantine: proven, reliable and production-ready, with no further breaking changes ever anticipated

Imperial is designed to be small. Its entire source code currently consists of 89 lines of code.

Building

Imperial can be built on Linux or Mac OS with Irk, by running the irk script in the root directory:

./irk

This script will download irk the first time it is run, start a daemon process, and run the build. Subsequent invocations will be near-instantaneous.

Contributing

Contributors to Imperial are welcome and encouraged. New contributors may like to look for issues marked .

We suggest that all contributors read the Contributing Guide to make the process of contributing to Imperial easier.

Please do not contact project maintainers privately with questions. While it can be tempting to repsond to such questions, private answers cannot be shared with a wider audience, and it can result in duplication of effort.

Author

Imperial was designed and developed by Jon Pretty, and commercial support and training is available from Propensive OÜ.

Name

This project is particular to Linux operating systems, whos mascot is a penguin. While Imperial defines the layout of the operating system's own (little) empire, "Emperor" is also a species of penguin.

License

Imperial is copyright © 2022 Jon Pretty & Propensive OÜ, and is made available under the Apache 2.0 License.