Nix-shell shebang: Difference between revisions

From NixOS Wiki
imported>Milahu
add section: Performance
Klinger (talk | contribs)
 
(10 intermediate revisions by 9 users not shown)
Line 7: Line 7:
The first shebang line is always <code>#! /usr/bin/env nix-shell</code>.<br>
The first shebang line is always <code>#! /usr/bin/env nix-shell</code>.<br>
The second shebang line declares the script language and the script dependencies.
The second shebang line declares the script language and the script dependencies.
As of Nix 2.19.0 you can also use the new CLI <code>nix shell</code> and flakes to define shebangs. See [https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.html?highlight=shebang#shebang-interpreter docs].


== Examples ==
== Examples ==
Line 16: Line 18:
<syntaxHighlight lang="bash">
<syntaxHighlight lang="bash">
#! /usr/bin/env nix-shell
#! /usr/bin/env nix-shell
#! nix-shell -i bash
#! nix-shell -i bash -p bash


echo hello world
echo hello world
Line 36: Line 38:
<syntaxHighlight lang="python">
<syntaxHighlight lang="python">
#! /usr/bin/env nix-shell
#! /usr/bin/env nix-shell
#! nix-shell -i python3
#! nix-shell -i python3 -p python3


print("hello world")
print("hello world")
Line 54: Line 56:
image.save(path)
image.save(path)
print(ansicolor.green(f"done {path}"))
print(ansicolor.green(f"done {path}"))
</syntaxHighlight>
=== Rust ===
==== No dependencies ====
<syntaxHighlight lang="bash">
#!/usr/bin/env nix-shell
#![allow()] /*
#!nix-shell -i bash -p rustc
rsfile="$(readlink -f $0)"
binfile="/tmp/$(basename "$rsfile").bin"
rustc "$rsfile" -o "$binfile" --edition=2021 && exec "$binfile" $@ || exit $?
*/
fn main() {
    for argument in std::env::args().skip(1) {
        println!("{}", argument);
    };
    println!("{}", std::env::var("HOME").expect(""));
}
</syntaxHighlight>
==== With dependencies ====
uses [https://github.com/fornwall/rust-script rust-script]
<syntaxHighlight lang="bash">
#!/usr/bin/env nix-shell
//! ```cargo
//! [dependencies]
//! time = "0.1.25"
//! ```
/*
#!nix-shell -i rust-script -p rustc -p rust-script -p cargo
*/
fn main() {
    for argument in std::env::args().skip(1) {
        println!("{}", argument);
    };
    println!("{}", std::env::var("HOME").expect(""));
    println!("{}", time::now().rfc822z());
}
</syntaxHighlight>
=== Haskell ===
<syntaxHighlight lang="haskell">
#! /usr/bin/env nix-shell
#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [turtle])" -i runghc
{-# LANGUAGE OverloadedStrings #-}
import Turtle
main = echo "Hello world!"
</syntaxHighlight>
</syntaxHighlight>


Line 63: Line 119:
#! /usr/bin/env nix-shell
#! /usr/bin/env nix-shell
#! nix-shell -i bash
#! nix-shell -i bash
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.03.tar.gz
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/aed4b19d312525ae7ca9bceb4e1efe3357d0e2eb.tar.gz


echo hello world
echo hello world
</syntaxHighlight>
</syntaxHighlight>
== Flake ==
It is also possible to make it work for flake like in:
<syntaxHighlight lang="bash">
#!/usr/bin/env -S nix shell nixpkgs#bash nixpkgs#hello nixpkgs#cowsay --command bash
hello | cowsay
</syntaxHighlight>
The [https://nix.dev/manual/nix/2.19/command-ref/new-cli/nix3-shell doc] mentions that it should be possible to run more complex commands using multiple lines, but it does not work for me as reported [https://github.com/NixOS/nixpkgs/issues/280033 here].


== Performance ==
== Performance ==
Line 74: Line 142:
* [https://discourse.nixos.org/t/speeding-up-nix-shell-shebang/4048 Speeding up nix-shell shebang]
* [https://discourse.nixos.org/t/speeding-up-nix-shell-shebang/4048 Speeding up nix-shell shebang]
* [https://github.com/xzfc/cached-nix-shell cached-nix-shell] - Instant startup time for nix-shell
* [https://github.com/xzfc/cached-nix-shell cached-nix-shell] - Instant startup time for nix-shell
* [https://www.tweag.io/blog/2020-06-25-eval-cache/ Nix Flakes, Part 2: Evaluation caching - Tweag]


== See also ==
== See also ==
Line 81: Line 150:
* [https://gist.github.com/travisbhartwell/f972aab227306edfcfea nix-shell and Shebang Lines]
* [https://gist.github.com/travisbhartwell/f972aab227306edfcfea nix-shell and Shebang Lines]
* [https://notes.yukiisbo.red/posts/2021/07/Spice_up_with_Nix_Scripts.html Spice up with Nix: Scripts with magical dependencies]
* [https://notes.yukiisbo.red/posts/2021/07/Spice_up_with_Nix_Scripts.html Spice up with Nix: Scripts with magical dependencies]
[[Category:Nix]]
[[Category:Shell]]

Latest revision as of 21:58, 28 May 2024

You can use nix-shell as a script interpreter to

  • run scripts in arbitrary languages
  • provide dependencies with Nix

To do this, start the script with multiple shebang (#!) lines.
The first shebang line is always #! /usr/bin/env nix-shell.
The second shebang line declares the script language and the script dependencies.

As of Nix 2.19.0 you can also use the new CLI nix shell and flakes to define shebangs. See docs.

Examples

Bash

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

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

echo hello world

You can use nix-shell -p ... to add dependencies:

#! /usr/bin/env nix-shell
#! nix-shell -i bash -p imagemagick cowsay

# scale image by 50%
convert "$1" -scale 50% "$1.s50.jpg" &&
cowsay "done $1.q50.jpg"

Python

#! /usr/bin/env nix-shell
#! nix-shell -i python3 -p python3

print("hello world")
#! /usr/bin/env nix-shell
#! nix-shell -i python3 -p python3Packages.pillow python3Packages.ansicolor

# scale image by 50%
import sys, PIL.Image, ansicolor
path = sys.argv[1]
image = PIL.Image.open(path)
factor = 0.5
image = image.resize((round(image.width * factor), round(image.height * factor)))
path = path + ".s50.jpg"
image.save(path)
print(ansicolor.green(f"done {path}"))

Rust

No dependencies

#!/usr/bin/env nix-shell
#![allow()] /*
#!nix-shell -i bash -p rustc
rsfile="$(readlink -f $0)"
binfile="/tmp/$(basename "$rsfile").bin"
rustc "$rsfile" -o "$binfile" --edition=2021 && exec "$binfile" $@ || exit $?
*/
fn main() {
    for argument in std::env::args().skip(1) {
        println!("{}", argument);
    };
    println!("{}", std::env::var("HOME").expect(""));
}

With dependencies

uses rust-script

#!/usr/bin/env nix-shell
//! ```cargo
//! [dependencies]
//! time = "0.1.25"
//! ```
/*
#!nix-shell -i rust-script -p rustc -p rust-script -p cargo
*/
fn main() {
    for argument in std::env::args().skip(1) {
        println!("{}", argument);
    };
    println!("{}", std::env::var("HOME").expect(""));
    println!("{}", time::now().rfc822z());
}

Haskell

#! /usr/bin/env nix-shell
#! nix-shell -p "haskellPackages.ghcWithPackages (p: with p; [turtle])" -i runghc

{-# LANGUAGE OverloadedStrings #-}

import Turtle

main = echo "Hello world!"

Pinning nixpkgs

To pin nixpkgs to a specific version, add a third shebang line:

#! /usr/bin/env nix-shell
#! nix-shell -i bash
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/aed4b19d312525ae7ca9bceb4e1efe3357d0e2eb.tar.gz

echo hello world

Flake

It is also possible to make it work for flake like in:

#!/usr/bin/env -S nix shell nixpkgs#bash nixpkgs#hello nixpkgs#cowsay --command bash

hello | cowsay

The doc mentions that it should be possible to run more complex commands using multiple lines, but it does not work for me as reported here.


Performance

TODO ... why the startup delay? how to make it faster?

See also