Nix-shell shebang: default.nix: No such file or directory

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1

As I’ve only started using nix / nixos relatively recently, I usually use flakes and new-style nix commands. I swear I’ve used the nix-shell shebang trick before, but for some reason can’t get it to work today – keep getting an error about it expecting default.nix and not finding it.

After reading https://nixos.wiki/wiki/Nix-shell_shebang

$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 5.15.85, NixOS, 22.11 (Raccoon), 22.11.20221224.dac57a4`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.11.1`
 - channels(root): `"nixos-22.11"`
 - channels(n8henrie): `"nixpkgs-22.11"`
 - nixpkgs: `/home/n8henrie/.nix-defexpr/channels/nixpkgs`
$ cat <<'EOF' > foo.sh
#! /usr/bin/env nix-shell
#! nix-shell -i bash

printf "hello world\n"
EOF
$ chmod +x ./foo.sh
$ ./foo.sh
error: getting status of '/tmp/tmp.bIWspg0FPp/default.nix': No such file or directory
$ $PWD/foo.sh
error: getting status of '/tmp/tmp.bIWspg0FPp/default.nix': No such file or directory
$ bash foo.sh 
hello world

Seeing same behavior on MacOS (aarch64) and NixOS (x86_64).

This thread is a little hard to follow but looks related: . / c u r s e d . n i x - #7 by deliciouslytyped, which is why I tried the absolute path (with $PWD).

Why am I not able to run ./foo.sh here?

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2

You forgot the -p bash part.

Given that bash is part of stdenv, you can probably get away with some other -p argument, but you need at least one, so that you’re invoking the right use mode of nix-shell.

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3

tejing is giving you the right advice, but to clarify: without another -p flag, nix-shell is trying to run shell.nix, just like a bare nix-shell invocation.

If it doesn’t find shell.nix, it falls back to default.nix.

When it doesn’t find that, it errors.

4

Interesting, I thought -p was for dependencies, and -i bash would imply -p bash.

The wiki entry seems to read that way. Should I edit it? (I’d be happy to.)

https://nixos.wiki/wiki/Nix-shell_shebang#Bash

To run bash scripts, set the interpreter with -i bash

#! /usr/bin/env nix-shell
#! nix-shell -i bash

echo hello world

It sure looks like my test script above should work, right?

5

They’re separate namespaces. Not every package has the same name as its binary, and there’s no dependable database to associate them. For example, how would nix-shell -i awk know it needs -p gawk? (For that matter, sometimes multiple packages provide the same binary name…)

Yeah, that’s wrong, please do fix that.

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6

There is an effort to make a tutorial for nix-shell in the “new” documentation add tutorial for nix-shell in shebang by rapenne-s · Pull Request #325 · NixOS/nix.dev · GitHub

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