#command #line #arguments #environment #config


A library to unify commandline arguments with config files and environment variables. And make it easier for users to tell your program how to behave across the three main input sources

6 releases

0.2.0 Dec 23, 2021
0.1.6 Dec 21, 2021
0.1.5 May 28, 2020
0.1.4 Apr 7, 2020
0.1.0 May 6, 2019

#226 in Configuration

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213 downloads per month
Used in 3 crates

MIT license

753 lines

Clap Conf

A library for Handling Configuration files, Command Line arguments, and Environment variables together.


There are three main ways programs get operation parameters when initializing.

  • Command Line Arguments.
  • Configuration files.
  • Environment Variables.

If you only want command line arguments Clap is an awesome project, and helps your command line program give such a great and clear user experience.

However if you want your program to handle all three of these you have your work cut out for you.

Each of these behave in different ways but often you want to be able to work with one of these but fall back on the others if the first is not supplied.

For example. Assuming you have built a clap matches object

//without clap conf but with clap.

//This code ignores the fact that env returns String,(and has to)
//but most config files and clap returns &str Which makes it even more tricky to handle
let filename = clap_matches.value_of("filename").unwrap_or(

clap_conf provides a wrapper that handles this so that results can be collected using a builder like pattern.

use clap_conf::prelude::*;

//once at the top of the file.
let cfg = with_toml_env(&clap_matches,&["priority/config/location","another/possible/location"]);

//something like this for every item.
let filename = cfg.grab().arg("filename").conf("filename").env("PROG_FILENAME").def("None");

//Or if you do not want to use a default and instead return an option.
let filename = cfg.grab().arg("filename").conf("filename").env("PROG_FILENAME").done();

clap_conf can also handle nested structures in your toml file.

let nested = cfg.grab().conf("a.b.nested_property").done();

Combining typed values was always going to be tricky, as the CLI and clap expect you to parse the result as you wish, but Toml does this for you. So for non string properties, it converts them back to string again.

It's not ideal, but it's better than nothing.



Now uses std::error::Error;


Added a new method to ConfError called add_info(self, &str)->Self So you can lazily add info to the message Added .req() to LocalGrabber;

Addded a MultiGrabber so getting arrays out is much simpler: use grab_multi() like you would use grab() or grab local()


Added .req(), and ask_default() to the Grabber.


Added Localizer and now wraps toml Value in localizer for with_toml_env Added Local Grabber so grab_local() should return a path, local to the config file selected


~54K SLoC