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


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

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

Synopsis
       nix shell [option<?>] installables<?>

Examples
       o  Start a shell providing youtube-dl from the nixpkgs flake:

       # nix shell nixpkgs#youtube-dl
       # youtube-dl --version
       2020.11.01.1

       o  Start a shell providing GNU Hello from NixOS 20.03:

       # nix shell nixpkgs/nixos-20.03#hello

       o  Run GNU Hello:

       # nix shell nixpkgs#hello --command hello --greeting 'Hi everybody!'
       Hi everybody!

       o  Run multiple commands in a shell environment:

       # nix shell nixpkgs#gnumake --command sh -c "cd src && make"

       o  Run GNU Hello in a chroot store:

       # nix shell --store ~/my-nix nixpkgs#hello --command hello

       o  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.

Description
       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.

Use as a #!-interpreter
       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 ])

Options
       o  --command / -c command args

          Command and arguments to be executed, defaulting to $SHELL

       o  --ignore-environment / -i

          Clear the entire environment (except those specified with --keep).

       o  --keep / -k name

          Keep the environment variable name.

       o  --stdin

          Read installables from the standard input. No default installable
          applied.

       o  --unset / -u name

          Unset the environment variable name.

   Common evaluation options
       o  --arg name expr

          Pass the value expr as the argument name to Nix functions.

       o  --arg-from-file name path

          Pass the contents of file path as the argument name to Nix
          functions.

       o  --arg-from-stdin name

          Pass the contents of stdin as the argument name to Nix functions.

       o  --argstr name string

          Pass the string string as the argument name to Nix functions.

       o  --debugger

          Start an interactive environment if evaluation fails.

       o  --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.

       o  --impure

          Allow access to mutable paths and repositories.

       o  --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.

       o  --override-flake original-ref resolved-ref

          Override the flake registries, redirecting original-ref to resolved-
          ref.

   Common flake-related options
       o  --commit-lock-file

          Commit changes to the flake's lock file.

       o  --inputs-from flake-url

          Use the inputs of the specified flake as registry entries.

       o  --no-registries

          Don't allow lookups in the flake registries.

                 DEPRECATED

                 Use --no-use-registries instead.

       o  --no-update-lock-file

          Do not allow any updates to the flake's lock file.

       o  --no-write-lock-file

          Do not write the flake's newly generated lock file.

       o  --output-lock-file flake-lock-path

          Write the given lock file instead of flake.lock within the top-level
          flake.

       o  --override-input input-path flake-url

          Override a specific flake input (e.g. dwarffs/nixpkgs). This implies
          --no-write-lock-file.

       o  --recreate-lock-file

          Recreate the flake's lock file from scratch.

                 DEPRECATED

                 Use nix flake update instead.

       o  --reference-lock-file flake-lock-path

          Read the given lock file instead of flake.lock within the top-level
          flake.

       o  --update-input input-path

          Update a specific flake input (ignoring its previous entry in the
          lock file).

                 DEPRECATED

                 Use nix flake update instead.

   Logging-related options
       o  --debug

          Set the logging verbosity level to `debug'.

       o  --log-format format

          Set the format of log output; one of raw, internal-json, bar or
          bar-with-logs.

       o  --print-build-logs / -L

          Print full build logs on standard error.

       o  --quiet

          Decrease the logging verbosity level.

       o  --verbose / -v

          Increase the logging verbosity level.

   Miscellaneous global options
       o  --help

          Show usage information.

       o  --offline

          Disable substituters and consider all previously downloaded files
          up-to-date.

       o  --option name value

          Set the Nix configuration setting name to value (overriding
          nix.conf).

       o  --refresh

          Consider all previously downloaded files out-of-date.

       o  --repair

          During evaluation, rewrite missing or corrupted files in the Nix
          store. During building, rebuild missing or corrupted store paths.

       o  --version

          Show version information.

   Options that change the interpretation of installables
       o  --expr expr

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

       o  --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.

                                                                 nix3-shell(1)