nurl
A CLI tool that automatically generates Nix fetcher calls from repository URLs, simplifying package definitions.
What is nurl?
nurl is a command-line tool that automatically generates Nix fetcher expressions from repository URLs. It solves the problem of manually writing and maintaining boilerplate Nix code for fetching dependencies by inferring the correct fetcher, retrieving the hash, and producing a complete expression.
Nix users and package maintainers who need to create or update Nix package definitions that fetch sources from various repositories and package registries.
Developers choose nurl because it automates a tedious part of Nix packaging, reduces errors in hash generation, supports a wide range of fetchers, and integrates well with tools like nix-init for broader package generation workflows.
Overview
Generate Nix fetcher calls from URLs [maintainer=@figsoda]
Use Cases
Best For
- Generating fetchFromGitHub calls for GitHub repositories
- Creating Nix expressions for crates from crates.io
- Fetching Python packages from PyPI in Nix
- Automating fetcher calls for GitLab, Bitbucket, or SourceHut repos
- Reducing boilerplate when writing Nix package definitions
- Quickly testing fetcher expressions without manual hash calculation
Not Ideal For
- Projects requiring full Nix package definitions with build phases and dependencies, as nurl only generates fetcher calls
- Users who need fine-grained control over file attributes or advanced configuration options like those in nix-prefetch
- Environments with restricted or no network access, since nurl must fetch hashes online
- Non-standard repository URLs where automatic fetcher inference might fail, necessitating manual overrides
Pros & Cons
Pros
Detects the correct Nix fetcher from the URL, such as fetchFromGitHub for GitHub repos, reducing manual errors. The README lists 18+ supported fetchers including fetchCrate and fetchPypi.
Fetches and includes the content hash in the output expression, ensuring reproducibility. It uses faster alternatives to Fixed-Output Derivations when possible for improved performance.
Offers JSON output, custom indentation, and argument overwrites, as shown with flags like --json and --overwrite. This allows seamless integration into various packaging workflows.
Supports 18+ fetchers from platforms like GitHub, GitLab, PyPI, and crates.io, making it versatile for diverse package sources. The --list-fetchers option enumerates all available fetchers.
Cons
Compared to nix-prefetch, nurl is less configurable and lacks support for file attributes, as noted in the README comparison, which may hinder advanced use cases.
Requires internet access to fetch hashes, making it unsuitable for offline environments or private repos without authentication workarounds.
Automatic fetcher inference can fail for obscure or custom URLs, forcing users to manually specify fetchers with --fetcher, adding complexity.
Frequently Asked Questions
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