Man page - nix3-env-shell(1)

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Manual

nix3-env-shell

Name
Synopsis
Examples
Description
Use as a #!-interpreter
Options
Common evaluation options
Common flake-related options
Logging-related options
Miscellaneous global options
Options that change environment variables
Options that change the interpretation of installables

Warning
This program is experimental and its interface is subject to change.

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

Note that it’s necessary to specify bash explicitly because your default shell (e.g. /bin/bash) generally will not exist in the chroot.

Description

nix shell runs a command in an environment in which the $PATH variable provides the specified installables . If no command is specified, it starts the default shell of your user account specified by $SHELL.

Use as a #!-interpreter

You can use nix as a script interpreter to allow scripts written in arbitrary languages to obtain their own dependencies via Nix. This is done by starting the script with the following lines:

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

where real-interpreter is the “real” script interpreter that will be invoked by nix shell after it has obtained the dependencies and initialised the environment, and installables are the attribute names of the dependencies in Nixpkgs.

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.

For example, here is 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.

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 want to 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 .

Common flake-related options

•

--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). 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.

Logging-related options

•

--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 will be read from standard input. Implies --impure.

Note

See man nix.conf for overriding configuration settings with command line flags.