It requires the programs `curl`, `xml2json`, and `jq`.
It also requires the `bash` interpreter.
If any of these dependencies are not present on the system running the script, it will fail partially or altogether.
With Nix, we can declare all dependencies explicitly, and produce a script that will always run on any machine that supports Nix and the required packages taken from Nixpkgs.
It takes a command name as argument and will run the first executable by that name it finds in the directories listed in the environment variable `$PATH`.
More details on the options can be found in the [`nix-shell` reference documentation](https://nixos.org/manual/nix/stable/command-ref/nix-shell.html#options).
With the `-p` option we specify the packages required for the script to run.
The command `xml2json` is provided by the package `python3Packages.xmljson`, while `bash`, `jq`, and `curl` are provided by packages of the same name. `cacert` must be present for SSL authentication to work. Use [search.nixos.org](https://search.nixos.org/packages) to find packages providing the program you need.
- {ref}`reading-nix-language` to learn about the Nix language, which is used to declare packages and configurations.
- {ref}`declarative-reproducible-envs` to create reproducible shell environments with a declarative configuration file.
- [Garbage Collection](https://nixos.org/manual/nix/stable/package-management/garbage-collection.html) – free up storage used by the programs made available through Nix