nix3-shell(1) General Commands Manual nix3-shell(1)

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

nix shell - run a shell in which the specified packages are available

nix shell [option…] installables…

•
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!
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Run multiple commands in a shell environment:
# nix shell nixpkgs#gnumake --command sh -c "cd src && make"
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Run GNU Hello in a chroot store:
# nix shell --store ~/my-nix nixpkgs#hello --command hello
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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.

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.

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 ])

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--command / -c command args
Command and arguments to be executed, defaulting to $SHELL
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--ignore-environment / -i
Clear the entire environment (except those specified with --keep).
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--keep / -k name
Keep the environment variable name.
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--stdin
Read installables from the standard input. No default installable applied.
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--unset / -u name
Unset the environment variable name.

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--arg name expr
Pass the value expr as the argument name to Nix functions.
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--arg-from-file name path
Pass the contents of file path as the argument name to Nix functions.
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--arg-from-stdin name
Pass the contents of stdin as the argument name to Nix functions.
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--argstr name string
Pass the string string as the argument name to Nix functions.
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--debugger
Start an interactive environment if evaluation fails.
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--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.
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--impure
Allow access to mutable paths and repositories.
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--include / -I path
Add path to the Nix search path. The Nix search path is initialized from the colon-separated NIX_PATH environment variable, and is used to look up the location of Nix expressions using paths enclosed in angle brackets (i.e., <nixpkgs>).
For instance, passing
-I /home/eelco/Dev
-I /etc/nixos
will cause Nix to look for paths relative to /home/eelco/Dev and /etc/nixos, in that order. This is equivalent to setting the NIX_PATH environment variable to
/home/eelco/Dev:/etc/nixos
It is also possible to match paths against a prefix. For example, passing
-I nixpkgs=/home/eelco/Dev/nixpkgs-branch
-I /etc/nixos
will cause Nix to search for <nixpkgs/path> in /home/eelco/Dev/nixpkgs-branch/path and /etc/nixos/nixpkgs/path.
If a path in the Nix search path starts with http:// or https://, it is interpreted as the URL of a tarball that will be downloaded and unpacked to a temporary location. The tarball must consist of a single top-level directory. For example, passing
-I nixpkgs=https://github.com/NixOS/nixpkgs/archive/master.tar.gz
tells Nix to download and use the current contents of the master branch in the nixpkgs repository.
The URLs of the tarballs from the official nixos.org channels (see the manual page for nix-channel) can be abbreviated as channel:<channel-name>. For instance, the following two flags are equivalent:
-I nixpkgs=channel:nixos-21.05
-I nixpkgs=https://nixos.org/channels/nixos-21.05/nixexprs.tar.xz
You can also fetch source trees using flake URLs and add them to the search path. For instance,
-I nixpkgs=flake:nixpkgs
specifies that the prefix nixpkgs shall refer to the source tree downloaded from the nixpkgs entry in the flake registry. Similarly,
-I nixpkgs=flake:github:NixOS/nixpkgs/nixos-22.05
makes <nixpkgs> refer to a particular branch of the NixOS/nixpkgs repository on GitHub.
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--override-flake original-ref resolved-ref
Override the flake registries, redirecting original-ref to resolved-ref.
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--commit-lock-file
Commit changes to the flake’s lock file.
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--inputs-from flake-url
Use the inputs of the specified flake as registry entries.
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--no-registries
Don’t allow lookups in the flake registries.
DEPRECATED
Use --no-use-registries instead.
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--no-update-lock-file
Do not allow any updates to the flake’s lock file.
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--no-write-lock-file
Do not write the flake’s newly generated lock file.
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--output-lock-file flake-lock-path
Write the given lock file instead of flake.lock within the top-level flake.
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--override-input input-path flake-url
Override a specific flake input (e.g. dwarffs/nixpkgs). This implies --no-write-lock-file.
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--recreate-lock-file
Recreate the flake’s lock file from scratch.
DEPRECATED
Use nix flake update instead.
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--reference-lock-file flake-lock-path
Read the given lock file instead of flake.lock within the top-level flake.
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--update-input input-path
Update a specific flake input (ignoring its previous entry in the lock file).
DEPRECATED
Use nix flake update instead.
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--debug
Set the logging verbosity level to ‘debug’.
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--log-format format
Set the format of log output; one of raw, internal-json, bar or bar-with-logs.
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--print-build-logs / -L
Print full build logs on standard error.
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--quiet
Decrease the logging verbosity level.
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--verbose / -v
Increase the logging verbosity level.

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

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--expr expr
Interpret installables as attribute paths relative to the Nix expression expr.
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--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.