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.
-
--commandcmd
In the environment of the derivation, run the shell command cmd. This command is executed in an interactive shell. (Use--runto use a non-interactive shell instead.) However, a call toexitis implicitly added to the command, so the shell will exit after running the command. To prevent this, addreturnat the end; e.g.--command "echo Hello; return"will printHelloand then drop you into the interactive shell. This can be useful for doing any additional initialisation. -
--runcmd
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. -
--excluderegexp
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 particularHOME,USERandDISPLAY, are retained. -
--packages/-ppackages…
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 openjdkwill start a shell in which the packages denoted by the attribute nameslibjpegandopenjdkare present. -
-iinterpreter
The chained script interpreter to be invoked bynix-shell. Only applicable in#!-scripts (described below). -
--keepname
When a--pureshell 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 thebashfound in<nixpkgs>, falling back to thebashfound inPATHif 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 ]; } ""