attr-cmd

Build shell commands from Nix attribute sets.

lib.attr-cmd.exec

exec :: AttrSet -> AttrSet

exec transforms a nested attribute set <input> into a flat attribute set <output>. For each attribute <attr> of <input> at the attribute path <root> . [...] . <attr> that evaluates to a derivation, it creates an attribute <root> in <output>. All other attribute paths are ignored.

Example

Transformation of attributes

{ lib, attr-cmd }:
let
  input = {
    a.b.c = drv;
    d.e.f = drv';
    g.h.i = "ignored";
  };
  output = attr-cmd.exec input;
in
{
  inherit = output;
  executable = lib.getExe output.a;
}

{ output = { a = drv''; d = drv'''; }; executable = "/nix/store/...-a/bin/a"}

Each attribute <root> in <output> is a derivation that produces an executable /bin/<root>. Such an executable <root> accepts command line words that correspond to attribute paths in <attrs-in> starting from <root>. The final command line word <attr> executes the meta.mainProgram (or /bin/<attr>) from the derivation's bin (or out) output at the corresponding attribute <attr> from <input>.

After adding the derivations from <output> to the environment, run the executable <attr> by specifying its attribute path as command line arguments:

<root> ... <attr> [<arguments>]...

Help will be shown for intermediate subcommands, displaying meta.description on a derivation or attribute set if available.

Example

Create a command from a derivation in an attribute set

Declare a nested attribute set foo with a derivation baz as a leaf attribute, and pass that attribute set to attr-cmd:

# ./default.nix
{
  sources ? import ./npins,
  system ? builtins.currentSystem,
  pkgs ? import sources.nixpkgs { inherit system; config = { }; overlays = [ ]; },
  attr-cmd ? pkgs.callPackage "${sources.attr-cmd}/lib.nix" {};
}:
let
  lib = pkgs.lib // attr-cmd.lib
lib
rec {
  foo.bar.baz = pkgs.writeScriptBin "baz" "echo success $@";
  commands = lib.attr-cmd.exec { inherit foo; }; ;
  shell = pkgs.mkShellNoCC {
    packages = builtins.attrValues commands ++ [
      pkgs.npins
    ];
  };
}

The values of the resulting attribute set commands are now derivations that create executables:

$ nix-shell -p npins --run "npins init"
$ nix-shell
[nix-shell:~]$ foo bar baz
success
[nix-shell:~]$ foo bar baz or else
success or else