Provided by: nix-bin_2.6.0+dfsg-3_amd64 
Name
nix-shell - start an interactive shell based on a Nix expression
Synopsis
nix-shell [--arg name value] [--argstr name value] [{--attr | -A} attrPath] [--command
cmd] [--run cmd] [--exclude regexp] [--pure] [--keep name] {{--packages | -p} {packages |
expressions} … | [path]}
Description
The command nix-shell will build the dependencies of the specified derivation, but not the
derivation itself. It will then start an interactive shell in which all environment
variables defined by the derivation path have been set to their corresponding values, and
the script $stdenv/setup has been sourced. This is useful for reproducing the environment
of a derivation for development.
If path is not given, nix-shell defaults to shell.nix if it exists, and default.nix
otherwise.
If 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 include a single
top-level directory containing at least a file named default.nix.
If the derivation defines the variable shellHook, it will be run after $stdenv/setup has
been sourced. Since this hook is not executed by regular Nix builds, it allows you to
perform initialisation specific to nix-shell. For example, the derivation attribute
shellHook =
''
echo "Hello shell"
export SOME_API_TOKEN="$(cat ~/.config/some-app/api-token)"
'';
will cause nix-shell to print Hello shell and set the SOME_API_TOKEN environment variable
to a user-configured value.
Options
All options not listed here are passed to nix-store --realise, except for --arg and --attr
/ -A which are passed to nix-instantiate.
• --command cmd
In the environment of the derivation, run the shell command cmd. This command is
executed in an interactive shell. (Use --run to use a non-interactive shell instead.)
However, a call to exit is implicitly added to the command, so the shell will exit after
running the command. To prevent this, add return at the end; e.g. --command "echo
Hello; return" will print Hello and then drop you into the interactive shell. This can
be useful for doing any additional initialisation.
• --run cmd
Like --command, but executes the command in a non-interactive shell. This means (among
other things) that if you hit Ctrl-C while the command is running, the shell exits.
• --exclude regexp
Do not build any dependencies whose store path matches the regular expression regexp.
This option may be specified multiple times.
• --pure
If this flag is specified, the environment is almost entirely cleared before the
interactive shell is started, so you get an environment that more closely corresponds to
the “real” Nix build. A few variables, in particular HOME, USER and DISPLAY, are
retained.
• --packages / -p packages…
Set up an environment in which the specified packages are present. The command line
arguments are interpreted as attribute names inside the Nix Packages collection. Thus,
nix-shell -p libjpeg openjdk will start a shell in which the packages denoted by the
attribute names libjpeg and openjdk are present.
• -i interpreter
The chained script interpreter to be invoked by nix-shell. Only applicable in #!-scripts
(described below).
• --keep name
When a --pure shell is started, keep the listed environment variables.
The following common options are supported:
Environment variables
• NIX_BUILD_SHELL
Shell used to start the interactive environment. Defaults to the bash found in
<nixpkgs>, falling back to the bash found in PATH if not found.
Examples
To build the dependencies of the package Pan, and start an interactive shell in which to
build it:
$ nix-shell '<nixpkgs>' -A pan
[nix-shell]$ eval ${unpackPhase:-unpackPhase}
[nix-shell]$ cd pan-*
[nix-shell]$ eval ${configurePhase:-configurePhase}
[nix-shell]$ eval ${buildPhase:-buildPhase}
[nix-shell]$ ./pan/gui/pan
The reason we use form eval ${configurePhase:-configurePhase} here is because those
packages that override these phases do so by exporting the overridden values in the
environment variable of the same name. Here bash is being told to either evaluate the
contents of ‘configurePhase’, if it exists as a variable, otherwise evaluate the
configurePhase function.
To clear the environment first, and do some additional automatic initialisation of the
interactive shell:
$ nix-shell '<nixpkgs>' -A pan --pure \
--command 'export NIX_DEBUG=1; export NIX_CORES=8; return'
Nix expressions can also be given on the command line using the -E and -p flags. For
instance, the following starts a shell containing the packages sqlite and libX11:
$ nix-shell -E 'with import <nixpkgs> { }; runCommand "dummy" { buildInputs = [ sqlite xorg.libX11 ]; } ""'
A shorter way to do the same is:
$ nix-shell -p sqlite xorg.libX11
[nix-shell]$ echo $NIX_LDFLAGS
… -L/nix/store/j1zg5v…-sqlite-3.8.0.2/lib -L/nix/store/0gmcz9…-libX11-1.6.1/lib …
Note that -p accepts multiple full nix expressions that are valid in the buildInputs = [
... ] shown above, not only package names. So the following is also legal:
$ nix-shell -p sqlite 'git.override { withManual = false; }'
The -p flag looks up Nixpkgs in the Nix search path. You can override it by passing -I or
setting NIX_PATH. For example, the following gives you a shell containing the Pan package
from a specific revision of Nixpkgs:
$ nix-shell -p pan -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/8a3eea054838b55aca962c3fbde9c83c102b8bf2.tar.gz
[nix-shell:~]$ pan --version
Pan 0.139
Use as a #!-interpreter
You can use nix-shell 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-shell
#! nix-shell -i real-interpreter -p packages
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 packages are
the attribute names of the dependencies in Nixpkgs.
The lines starting with #! nix-shell specify nix-shell 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-shell
#! nix-shell -i python -p python pythonPackages.prettytable
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-shell
#! nix-shell -i perl -p perl perlPackages.HTMLTokeParserSimple perlPackages.LWP
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-shell
#! nix-shell -i bash -p "terraform.withPlugins (plugins: [ plugins.openstack ])"
terraform apply
Note
You must use double quotes (") 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 20.03 stable branch):
#! /usr/bin/env nix-shell
#! nix-shell -i runghc -p "haskellPackages.ghcWithPackages (ps: [ps.download-curl ps.tagsoup])"
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-20.03.tar.gz
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 -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/0672315759b3e15e2121365f067c1c8c56bb4722.tar.gz
The examples above all used -p to get dependencies from Nixpkgs. 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-shell
#! nix-shell deps.nix -i python
where the file deps.nix in the same directory as the #!-script contains:
with import <nixpkgs> {};
runCommand "dummy" { buildInputs = [ python pythonPackages.prettytable ]; } ""
nix-shell(1)