nix3-env-shell(1)

📦
version 2.35.3 · 9 versions
, in fedora 44

💅 nix3-env-shell(1) 💅

okay so bestie, welcome to the manual page for nix env shell — it's part of the General Commands Manual and honestly? it's giving ✨portal to a whole new environment✨.

🚨 Warning 🚨 This program is experimental and its interface is subject to change. so like, it's iconic but it's also in its experimental era, no cap.

🌸 Name 🌸

nix env shell — run a shell in which the specified packages are available 🦋

✨ Synopsis ✨

nix env shell [option…] installables…

🎀 Examples 🎀

  • Start a shell providing youtube-dl from the nixpkgs flake:
# nix shell nixpkgs#youtube-dl
# youtube-dl --version
2020.11.01.1
  • Start a shell providing GNU Hello from NixOS 20.03:
# nix shell nixpkgs/nixos-20.03#hello
  • Run GNU Hello:
# nix shell nixpkgs#hello --command hello --greeting 'Hi everybody!'
Hi everybody!
  • Run multiple commands in a shell environment:
# nix shell nixpkgs#gnumake --command sh -c "cd src && make"
  • Run GNU Hello in a chroot store:
# nix shell --store ~/my-nix nixpkgs#hello --command hello
  • Start a shell providing GNU Hello in a chroot store:
# nix shell --store ~/my-nix nixpkgs#hello nixpkgs#bashInteractive --command bash
💀 psst — you gotta specify bash explicitly because your default shell (like /bin/bash) generally will not exist in the chroot. it's not a vibe, it's just how it is bestie.

💖 Description 💖

nix shell runs a command in an environment where the $PATH variable provides the specified installables . If you don't give it a command, it starts the default shell of your user account, which is specified by $SHELL. slay.

🐚 Use as a #!-interpreter 🐚

You can use nix as a script interpreter so scripts written in literally any language can grab their own dependencies via Nix. the way you do it? start the script with these lines:

#! /usr/bin/env nix
#! nix shell installables --command real-interpreter

where real-interpreter is the "real" script interpreter that gets invoked by nix shell after it's snagged the dependencies and initialised the environment, and installables are the attribute names of the dependencies in Nixpkgs. it's giving dependency-glow-up ✨

The lines starting with #! nix specify options (see above 👀). Note that you cannot write #! /usr/bin/env nix shell -i ... because many operating systems only allow one argument in #! lines. so rude of them tbh.

For example, here's a Python script that depends on Python and the prettytable package:

#! /usr/bin/env nix
#! nix shell github:tomberek/-#python3With.prettytable --command python

import prettytable

# Print a simple table.
t = prettytable.PrettyTable(["N", "N^2"])
for n in range(1, 10): t.add_row([n, n * n])
print(t)

Similarly, the following is a Perl script that specifies that it requires Perl and the HTML::TokeParser::Simple and LWP packages:

#! /usr/bin/env nix
#! nix shell github:tomberek/-#perlWith.HTMLTokeParserSimple.LWP --command perl -x

use HTML::TokeParser::Simple;

# Fetch nixos.org and print all hrefs.
my $p = HTML::TokeParser::Simple->new(url => 'http://nixos.org/');

while (my $token = $p->get_tag("a")) {
    my $href = $token->get_attr("href");
    print "$href\n" if $href;
}

Sometimes you need to pass a simple Nix expression to customize a package like Terraform:

#! /usr/bin/env nix
#! nix shell --impure --expr ``
#! nix with (import (builtins.getFlake ''nixpkgs'') {});
#! nix terraform.withPlugins (plugins: [ plugins.openstack ])
#! nix ``
#! nix --command bash

terraform "$@"
📝 Note 📝 You must use double backticks (``) when passing a simple Nix expression in a nix shell shebang. don't forget, bestie, or it's not gonna work 😭

Finally, using the merging of multiple nix shell shebangs, the following Haskell script uses a specific branch of Nixpkgs/NixOS (the 21.11 stable branch):

#!/usr/bin/env nix
#!nix shell --override-input nixpkgs github:NixOS/nixpkgs/nixos-21.11
#!nix github:tomberek/-#haskellWith.download-curl.tagsoup --command runghc

import Network.Curl.Download
import Text.HTML.TagSoup
import Data.Either
import Data.ByteString.Char8 (unpack)

-- Fetch nixos.org and print all hrefs.
main = do
  resp <- openURI "https://nixos.org/"
  let tags = filter (isTagOpenName "a") $ parseTags $ unpack $ fromRight undefined resp
  let tags' = map (fromAttrib "href") tags
  mapM_ putStrLn $ filter (/= "") tags'

If you wanna be even more precise, you can specify a specific revision of Nixpkgs:

#!nix shell --override-input nixpkgs github:NixOS/nixpkgs/eabc38219184cc3e04a974fe31857d8e0eac098d

You can also use a Nix expression to build your own dependencies. For example, the Python example could have been written as:

#! /usr/bin/env nix
#! nix shell --impure --file deps.nix -i python

where the file deps.nix in the same directory as the #!-script contains:

with import <nixpkgs> {};
python3.withPackages (ps: with ps; [ prettytable ])

🌈 Options 🌈

  • --command, -c command args — Command and arguments to be executed, defaulting to $SHELL
  • --stdin — Read installables from the standard input. No default installable applied.

🧮 Common evaluation options 🧮

  • --arg name expr — Pass the value expr as the argument name to Nix functions.
  • --arg-from-file name path — Pass the contents of file path as the argument name to Nix functions.
  • --arg-from-stdin name — Pass the contents of stdin as the argument name to Nix functions.
  • --argstr name string — Pass the string string as the argument name to Nix functions.
  • --debugger — Start an interactive environment if evaluation fails.
  • --eval-store store-url — The URL of the Nix store to use for evaluation, i.e. to store derivations (.drv files) and inputs referenced by them.
  • --impure — Allow access to mutable paths and repositories.
  • --include, -I path — Add path to search path entries used to resolve lookup paths.

This option may be given multiple times.

Paths added through -I take precedence over the nix-path configuration setting and the NIX_PATH environment variable.

  • --override-flake original-ref resolved-ref — Override the flake registries, redirecting original-ref to resolved-ref.
  • --commit-lock-file — Commit changes to the flake's lock file.
  • --inputs-from flake-url — Use the inputs of the specified flake as registry entries.
  • --no-registries — Don't allow lookups in the flake registries.
⚠️ DEPRECATED ⚠️ Use --no-use-registries instead.
  • --no-update-lock-file — Do not allow any updates to the flake's lock file.
  • --no-write-lock-file — Do not write the flake's newly generated lock file.
  • --output-lock-file flake-lock-path — Write the given lock file instead of flake.lock within the top-level flake.
  • --override-input input-path flake-url — Override a specific flake input (e.g. dwarffs/nixpkgs). The input path must not be empty. This implies --no-write-lock-file.
  • --recreate-lock-file — Recreate the flake's lock file from scratch.
⚠️ DEPRECATED ⚠️ Use nix flake update instead.
  • --reference-lock-file flake-lock-path — Read the given lock file instead of flake.lock within the top-level flake.
  • --update-input input-path — Update a specific flake input (ignoring its previous entry in the lock file).
⚠️ DEPRECATED ⚠️ Use nix flake update instead.
  • --debug — Set the logging verbosity level to 'debug'.
  • --log-format format — Set the format of log output; one of raw, internal-json, bar or bar-with-logs.
  • --print-build-logs, -L — Print full build logs on standard error.
  • --quiet — Decrease the logging verbosity level.
  • --verbose, -v — Increase the logging verbosity level.

🫶 Miscellaneous global options 🫶

  • --help — Show usage information.
  • --offline — Disable substituters and consider all previously downloaded files up-to-date.
  • --option name value — Set the Nix configuration setting name to value (overriding nix.conf).
  • --refresh — Consider all previously downloaded files out-of-date.
  • --repair — During evaluation, rewrite missing or corrupted files in the Nix store. During building, rebuild missing or corrupted store paths.
  • --version — Show version information.

🌿 Options that change environment variables 🌿

  • --ignore-env, -i — Clear the entire environment, except for those specified with --keep-env-var.
  • --keep-env-var, -k name — Keep the environment variable name, when using --ignore-env.
  • --set-env-var, -s name value — Sets an environment variable name with value.
  • --unset-env-var, -u name — Unset the environment variable name.

🧚 Options that change the interpretation of installables 🧚

  • --expr expr — Interpret installables as attribute paths relative to the Nix expression expr.
  • --file, -f file — Interpret installables as attribute paths relative to the Nix expression stored in file. If file is the character -, then a Nix expression is read from standard input. Implies --impure.
📝 Note 📝 See man nix.conf for overriding configuration settings with command line flags.

and that's the whole page bestie 💜 this came from the nix3-env-shell(1) manual, General Commands Manual edition — it's iconic, it's experimental, it's giving ✨flake energy✨. go forth and shell responsibly 🫶🌸

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