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)