knoopx/nix

Nix

Package manager and functional language for reproducible environments. Run any tool once without installing it permanently.

Running Packages

Execute a package from nixpkgs directly:

nix run nixpkgs#cowsay -- "Hello!"    # Run with arguments
nix run nixpkgs#hello                  # Simple command

For long-running services, wrap in tmux: tmux new -d 'nix run nixpkgs#some-server'.

Shell Environments

Create a temporary shell with specific tools:

nix shell nixpkgs#git nixpkgs#vim --command git --version

Evaluating Expressions

Debug and inspect Nix expressions in headless environments:

nix eval --expr '1 + 2'              # Simple expression
nix eval nixpkgs#hello.name          # Inspect an attribute
nix eval --file ./default.nix        # Evaluate a local file
nix eval --expr 'builtins.attrNames (import <nixpkgs> {})'  # List keys

Searching Packages

nix search nixpkgs python3           # Search by name or description

Formatting Nix Files

nix fmt                              # Format current directory
nix fmt -- --check                   # Check formatting without changes

Hash Utilities

Convert between hash formats:

# Convert SRI to nix32 format
nix hash convert --hash-algo sha256 --to nix32 sha256-ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=

# Convert nix32 to SRI
nix hash convert --hash-algo sha256 --from nix32 --to sri 1b8m03r63zqhnjf7l5wnldhh7c134ap5vpj0850ymkq1iyzicy5s

Prefetch a URL and get its hash:

nix-prefetch-url --unpack https://example.com/source.tar.gz

Shebang Scripts

Use Nix as a script interpreter:

#!/usr/bin/env nix
#! nix shell nixpkgs#bash nixpkgs#curl --command bash
curl -s https://example.com

Troubleshooting

• Broken builds: nix log <derivation> to see build output
• Dependency chains: nix why-depends nixpkgs#hello nixpkgs#glibc
• Bad cache: Add --no-substitute to force local build
• References: nix-store -q --references $(which program)

Related Skills

• nix-flakes: Reproducible builds with flake.nix
• nh: Cleaner interface for NixOS/Home Manager operations