Nix: Write Google ZX script that is invokable without the mjs extension - nix

Question

I want to write Google ZX scripts in an idiomatic way in Nix, but how can I do that? nixpkgs only offers writeShellScriptBin which is tied to bash as interpreter. How can I change the interpreter?

Answer 1

To solve it idiomatically, you could create a writeZxScriptBin attribute similar to writeShellScriptBin. Luckily, zx is already packaged in <nixpkgs>. Hence, we can write a zx-script-writer-bin.nix like this:
# This returns a writer that creates an executable Google ZX script in `<pkg>/bin/%name`
# with the provided content. Similar to `writeShellScriptBin`, it consumes the name of
# the script and the NodeJS/ZX-script content as parameters.
{ pkgs }:
name: text:
let
mjsBin = pkgs.writeTextFile {
name = "${name}-mjs";
executable = true;
# For Google ZX, the .mjs extension is mandatory.
destination = "/bin/${name}.mjs";
text = ''
#!${pkgs.zx}/bin/zx
${text}
'';
};
in
# Shebang script enables to call the zx-script without the .mjs version.
pkgs.writeTextFile {
name = "${name}";
executable = true;
destination = "/bin/${name}";
text = ''
#!${mjsBin}/bin/${name}.mjs
'';
}
We can invoke it like this:
$ nix-build -E "
let
pkgs = import <nixpkgs> {};
writeZxScriptBin = pkgs.callPackage ./write-zx-script-bin.nix {};
in
writeZxScriptBin \"foo\" ''
const a = 7
console.log(\`hello! sum=''\${3 + a}\`)
''" && result/bin/foo
Note that there is some escaping required. Alternatively, you can work with builtins.readFile to write the script code in pure JavaScript