3 min
Using a Nix Flake to load a default.nix from nixpkgs
Short Version
You can load a local default.nix
file taken from nixpkgs with the following flake.nix
:
{
description = "A very basic flake that can load a default.nix from nixpkgs";
inputs = {
nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
};
outputs = { self, nixpkgs }: let
pkgs = nixpkgs.legacyPackages.x86_64-linux;
in {
# Use callPackage to use the ./default.nix file
packages.x86_64-linux.default = pkgs.callPackage ./default.nix {};
};
}
Just change the callPackage
call to the path of the default.nix
and you are good to go.
Explanation
I wanted to play around with a default.nix
from nixpkgs locally in a Nix flake. However, I could only find the following command, that can be used to load a local default.nix
inside a nix-shell
:
nix-shell -p '
let
pkgs = import <nixpkgs> {};
in
pkgs.callPackage ./default.nix {}
'
However, I wanted to be able to load it as a Nix flake. And since I couldn’t find any instructions on how to that when I searched online, here’s a quick explanation of how to do it.
First, we need to initialize a flake:
nix flake init
This will create a basic flake.nix
in your current directory:
{
description = "A very basic flake";
inputs = {
nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
};
outputs = { self, nixpkgs }: {
packages.x86_64-linux.hello = nixpkgs.legacyPackages.x86_64-linux.hello;
packages.x86_64-linux.default = self.packages.x86_64-linux.hello;
};
}
To load a default.nix
from nixpkgs, for example the default.nix of nmap, we need to change the outputs. We set packages.x86_64-linux.default
to callPackage ./default.nix {}
, which will load the specified ./default.nix
:
{
description = "A very basic flake";
inputs = {
nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
};
outputs = { self, nixpkgs }: {
# Use callPackage to use the ./default.nix file
packages.x86_64-linux.default = nixpkgs.legacyPackages.x86_64-linux.callPackage ./default.nix {};
};
}
After this change, we can load the flake and work with nix shell
and enjoy nmap:
$ nmap --help
Nmap 7.94 ( https://nmap.org )
Usage: nmap [Scan Type(s)] [Options] {target specification}
TARGET SPECIFICATION:
Can pass hostnames, IP addresses, networks, etc.
Ex: scanme.nmap.org, microsoft.com/24, 192.168.0.1; 10.0.0-255.1-254
-iL <inputfilename>: Input from list of hosts/networks
-iR <num hosts>: Choose random targets
--exclude <host1[,host2][,host3],...>: Exclude hosts/networks
--excludefile <exclude_file>: Exclude list from file
HOST DISCOVERY:
-sL: List Scan - simply list targets to scan
-sn: Ping Scan - disable port scan
...
To make it a bit easier to read, we can define the variable pkgs
within a let expression and add a better description:
{
description = "A very basic flake that can load a default.nix from nixpkgs";
inputs = {
nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
};
outputs = { self, nixpkgs }: let
pkgs = nixpkgs.legacyPackages.x86_64-linux;
in {
# Use callPackage to use the ./default.nix file
packages.x86_64-linux.default = pkgs.callPackage ./default.nix {};
};
}