nix-shell 1 Nix nix-shell start an interactive shell based on a Nix expression 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 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 evaluated 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" ''; will cause nix-shell to print Hello shell. All options not listed here are passed to nix-store --realise, except for --arg and --attr / -A which are passed to nix-instantiate. See also . --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. Note that ~/.bashrc and (depending on your Bash installation) /etc/bashrc are still sourced, so any variables set there will affect the interactive shell. --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: NIX_BUILD_SHELL Shell used to start the interactive environment. Defaults to the bash found in PATH. 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]$ unpackPhase [nix-shell]$ cd pan-* [nix-shell]$ configurePhase [nix-shell]$ buildPhase [nix-shell]$ ./pan/gui/pan 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-channels/archive/8a3eea054838b55aca962c3fbde9c83c102b8bf2.tar.gz [nix-shell:~]$ pan --version Pan 0.139 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: 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 18.03 stable branch): 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-channels/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 ]; } ""