npins/readme.nix at master · andir/npins · GitHub

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{
  system ? builtins.currentSystem,
}:
let
  pins = import ./npins;
  pkgs = import pins.nixpkgs { inherit system; };
  npins = pkgs.callPackage ./default.nix { };
in
pkgs.runCommand "readme"
  {
    nativeBuildInputs = [ npins ];
    preferLocalBuild = true;

    raw = ./README.md.in;
  }
  ''
    set -euo pipefail
    content="$(cat $raw)"

    # Match "{{foo}}"
    regex='\{\{([^\}]*)\}\}'

    # Replace "{{foo}}" with "$(foo)", i.e. run the command
    while [[ $content =~ $regex ]]; do
      command="''${BASH_REMATCH[1]}"
      # Run the command, capture failure gracefully
      command="$($command 2>&1 || true)"

      content="''${content/"''${BASH_REMATCH[0]}"/"$command"}"
    done

    echo "$content" >> $out
  ''