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nix-shell(1) General Commands Manual nix-shell(1) Name nix-shell - start an interactive shell based on a Nix expression Synopsis nix-shell [--arg name value] [--argstr name value] [{--attr | -A} attr- Path] [--command cmd] [--run cmd] [--exclude regexp] [--pure] [--keep name] {{--packages | -p} {packages | expressions} | [path]} Disambiguation This man page describes the command nix-shell, which is distinct from nix shell. For documentation on the latter, run nix shell --help or see man nix3-shell. Description The command nix-shell will build the dependencies of the specified de- rivation, but not the derivation itself. It will then start an interac- tive 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 en- vironment 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 loca- tion. 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 $stdenv/setup has been sourced. Since this hook is not executed by reg- ular Nix builds, it allows you to perform initialisation specific to nix-shell. For example, the derivation attribute shellHook = '' echo "Hello shell" export SOME_API_TOKEN="$(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 implic- itly 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 in- teractive shell. This can be useful for doing any additional ini- tialisation. • --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 envi- ronment that more closely corresponds to the real Nix build. A few variables, in particular HOME, USER and DISPLAY, are retained. Note that the shell used to run commands is obtained from NIX_BUILD_SHELL <#env-NIX_BUILD_SHELL> / <nixpkgs> from NIX_PATH, and therefore not affected by --pure. • --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 --packages libjpeg openjdk will start a shell in which the packages denoted by the at- tribute names libjpeg and openjdk are present. • -i interpreter The chained script interpreter to be invoked by nix-shell. Only ap- plicable in #!-scripts (described below). • --keep name When a --pure shell is started, keep the listed environment vari- ables. Common Options Most Nix commands accept the following command-line options: • --help <#opt-help> Prints out a summary of the command syntax and exits. • --version <#opt-version> Prints out the Nix version number on standard output and exits. • --verbose <#opt-verbose> / -v Increases the level of verbosity of diagnostic messages printed on standard error. For each Nix operation, the information printed on standard output is well-defined; any diagnostic information is printed on standard error, never on standard output. This option may be specified repeatedly. Currently, the following verbosity levels exist: • 0 Errors only Only print messages explaining why the Nix invocation failed. • 1 Informational Print useful messages about what Nix is doing. This is the default. • 2 Talkative Print more informational messages. • 3 Chatty Print even more informational messages. • 4 Debug Print debug information. • 5 Vomit Print vast amounts of debug information. • --quiet <#opt-quiet> Decreases the level of verbosity of diagnostic messages printed on standard error. This is the inverse option to -v / --verbose. This option may be specified repeatedly. See the previous verbosity levels list. • --log-format <#opt-log-format> format This option can be used to change the output of the log format, with format being one of: • raw This is the raw format, as outputted by nix-build. • internal-json Outputs the logs in a structured manner. Warning While the schema itself is relatively stable, the format of the error-messages (namely of the msg-field) can change be- tween releases. • bar Only display a progress bar during the builds. • bar-with-logs Display the raw logs, with the progress bar at the bottom. • --no-build-output <#opt-no-build-output> / -Q By default, output written by builders to standard output and stan- dard error is echoed to the Nix command's standard error. This op- tion suppresses this behaviour. Note that the builder's standard output and error are always written to a log file in pre- fix/nix/var/log/nix. • --max-jobs <#opt-max-jobs> / -j number Sets the maximum number of build jobs that Nix will perform in par- allel to the specified number. Specify auto to use the number of CPUs in the system. The default is specified by the max-jobs con- figuration setting, which itself defaults to 1. A higher value is useful on SMP systems or to exploit I/O latency. Setting it to 0 disallows building on the local machine, which is useful when you want builds to happen only on remote builders. • --cores <#opt-cores> Sets the value of the NIX_BUILD_CORES environment variable in the invocation of builders. Builders can use this variable at their discretion to control the maximum amount of parallelism. For in- stance, in Nixpkgs, if the derivation attribute enableParallelBuild- ing is set to true, the builder passes the -jN flag to GNU Make. It defaults to the value of the cores configuration setting, if set, or 1 otherwise. The value 0 means that the builder should use all available CPU cores in the system. • --max-silent-time <#opt-max-silent-time> Sets the maximum number of seconds that a builder can go without producing any data on standard output or standard error. The de- fault is specified by the max-silent-time configuration setting. 0 means no time-out. • --timeout <#opt-timeout> Sets the maximum number of seconds that a builder can run. The de- fault is specified by the timeout configuration setting. 0 means no timeout. • --keep-going <#opt-keep-going> / -k Keep going in case of failed builds, to the greatest extent possi- ble. That is, if building an input of some derivation fails, Nix will still build the other inputs, but not the derivation itself. Without this option, Nix stops if any build fails (except for builds of substitutes), possibly killing builds in progress (in case of parallel or distributed builds). • --keep-failed <#opt-keep-failed> / -K Specifies that in case of a build failure, the temporary directory (usually in /tmp) in which the build takes place should not be deleted. The path of the build directory is printed as an informa- tional message. • --fallback <#opt-fallback> Whenever Nix attempts to build a derivation for which substitutes are known for each output path, but realising the output paths through the substitutes fails, fall back on building the derivation. The most common scenario in which this is useful is when we have registered substitutes in order to perform binary distribution from, say, a network repository. If the repository is down, the realisa- tion of the derivation will fail. When this option is specified, Nix will build the derivation instead. Thus, installation from bi- naries falls back on installation from source. This option is not the default since it is generally not desirable for a transient failure in obtaining the substitutes to lead to a full build from source (with the related consumption of resources). • --readonly-mode <#opt-readonly-mode> When this option is used, no attempt is made to open the Nix data- base. Most Nix operations do need database access, so those opera- tions will fail. • --arg <#opt-arg> name value This option is accepted by nix-env, nix-instantiate, nix-shell and nix-build. When evaluating Nix expressions, the expression evalua- tor will automatically try to call functions that it encounters. It can automatically call functions for which every argument has a de- fault value <../language/syntax.md#functions> (e.g., { argName ? defaultValue }: ...). With --arg, you can also call functions that have arguments without a default value (or override a default value). That is, if the evaluator encounters a function with an argument named name, it will call it with value value. For instance, the top-level default.nix in Nixpkgs is actually a function: { # The system (e.g., `i686-linux') for which to build the packages. system ? builtins.currentSystem ... }: ... So if you call this Nix expression (e.g., when you do nix-env --install --attr pkgname), the function will be called automati- cally using the value builtins.currentSystem <../language/builtins.md> for the system argument. You can override this using --arg, e.g., nix-env --install --attr pkg- name --arg system \"i686-freebsd\". (Note that since the argu- ment is a Nix string literal, you have to escape the quotes.) • --arg-from-file <#opt-arg-from-file> name path Pass the contents of file path as the argument name to Nix func- tions. • --arg-from-stdin <#opt-arg-from-stdin> name Pass the contents of stdin as the argument name to Nix functions. • --argstr <#opt-argstr> name value This option is like --arg, only the value is not a Nix expression but a string. So instead of --arg system \"i686-linux\" (the outer quotes are to keep the shell happy) you can say --argstr system i686-linux. • --attr <#opt-attr> / -A attrPath Select an attribute from the top-level Nix expression being evalu- ated. (nix-env, nix-instantiate, nix-build and nix-shell only.) The attribute path attrPath is a sequence of attribute names sepa- rated by dots. For instance, given a top-level Nix expression e, the attribute path xorg.xorgserver would cause the expression e.xorg.xorgserver to be used. See nix-env --install <../command- ref/nix-env/install.md> for some concrete examples. In addition to attribute names, you can also specify array indices. For instance, the attribute path foo.3.bar selects the bar attribute of the fourth element of the array in the foo attribute of the top- level expression. • --eval-store <#opt-eval-store> store-url The URL to the Nix store <../store/types/index.md#store-url-format> to use for evaluation, i.e. where to store derivations (.drv files) and inputs referenced by them. • --expr <#opt-expr> / -E Interpret the command line arguments as a list of Nix expressions to be parsed and evaluated, rather than as a list of file names of Nix expressions. (nix-instantiate, nix-build and nix-shell only.) For nix-shell, this option is commonly used to give you a shell in which you can build the packages returned by the expression. If you want to get a shell which contain the built packages ready for use, give your expression to the nix-shell --packages convenience flag instead. • -I / --include <#opt-I> path Add an entry to the list of search paths used to resolve lookup paths <../language/constructs/lookup-path.md>. This option may be given multiple times. Paths added through -I take precedence over the nix-path configura- tion setting <../command-ref/conf-file.md#conf-nix-path> and the NIX_PATH environment variable <../command-ref/env-common.md#env- NIX_PATH>. • --impure <#opt-impure> Allow access to mutable paths and repositories. • --option <#opt-option> name value Set the Nix configuration option name to value. This overrides set- tings in the Nix configuration file (see nix.conf5). • --repair <#opt-repair> Fix corrupted or missing store paths by redownloading or rebuilding them. Note that this is slow because it requires computing a cryp- tographic hash of the contents of every path in the closure of the build. Also note the warning under nix-store --repair-path. Note See man nix.conf <../command-ref/conf-file.md#command-line-flags> for overriding configuration settings with command line flags. Environment variables • NIX_BUILD_SHELL <#env-NIX_BUILD_SHELL> Shell used to start the interactive environment. Defaults to the bash from bashInteractive found in <nixpkgs>, falling back to the bash found in PATH if not found. Note The shell obtained using this method may not necessarily be the same as any shells requested in path. **Example Despite --pure, this invocation will not result in a fully reproducible shell environment: #!/usr/bin/env -S nix-shell --pure let pkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/854fdc68881791812eddd33b2fed94b954979a8e.tar.gz") {}; in pkgs.mkShell { buildInputs = pkgs.bashInteractive; } Common Environment Variables Most Nix commands interpret the following environment variables: • IN_NIX_SHELL <#env-IN_NIX_SHELL> Indicator that tells if the current environment was set up by nix- shell. It can have the values pure or impure. • NIX_PATH <#env-NIX_PATH> A colon-separated list of search path entries used to resolve lookup paths <../language/constructs/lookup-path.md>. This environment variable overrides the value of the nix-path con- figuration setting <../command-ref/conf-file.md#conf-nix-path>. It can be extended using the -I option <../command-ref/opt-com- mon.md#opt-I>. Example $ export NIX_PATH=`/home/eelco/Dev:nixos-config=/etc/nixos If NIX_PATH is set to an empty string, resolving search paths will always fail. Example $ NIX_PATH= nix-instantiate --eval '<nixpkgs>' error: file 'nixpkgs' was not found in the Nix search path (add it using $NIX_PATH or -I) • NIX_IGNORE_SYMLINK_STORE <#env-NIX_IGNORE_SYMLINK_STORE> Normally, the Nix store directory (typically /nix/store) is not al- lowed to contain any symlink components. This is to prevent impure builds. Builders sometimes canonicalise paths by resolving all sym- link components. Thus, builds on different machines (with /nix/store resolving to different locations) could yield different results. This is generally not a problem, except when builds are deployed to machines where /nix/store resolves differently. If you are sure that youre not going to do that, you can set NIX_IGNORE_SYMLINK_STORE to 1. Note that if youre symlinking the Nix store so that you can put it on another file system than the root file system, on Linux youre better off using bind mount points, e.g., $ mkdir /nix $ mount -o bind /mnt/otherdisk/nix /nix Consult the mount 8 manual page for details. • NIX_STORE_DIR <#env-NIX_STORE_DIR> Overrides the location of the Nix store (default prefix/store). • NIX_DATA_DIR <#env-NIX_DATA_DIR> Overrides the location of the Nix static data directory (default prefix/share). • NIX_LOG_DIR <#env-NIX_LOG_DIR> Overrides the location of the Nix log directory (default pre- fix/var/log/nix). • NIX_STATE_DIR <#env-NIX_STATE_DIR> Overrides the location of the Nix state directory (default pre- fix/var/nix). • NIX_CONF_DIR <#env-NIX_CONF_DIR> Overrides the location of the system Nix configuration directory (default sysconfdir/nix, i.e. /etc/nix on most systems). • NIX_CONFIG <#env-NIX_CONFIG> Applies settings from Nix configuration from the environment. The content is treated as if it was read from a Nix configuration file. Settings are separated by the newline character. • NIX_USER_CONF_FILES <#env-NIX_USER_CONF_FILES> Overrides the location of the Nix user configuration files to load from. The default are the locations according to the XDG Base Directory Specification <https://specifications.freedesktop.org/basedir- spec/basedir-spec-latest.html>. See the XDG Base Directories <#xdg- base-directories> sub-section for details. The variable is treated as a list separated by the : token. • TMPDIR <#env-TMPDIR> Use the specified directory to store temporary files. In particular, this includes temporary build directories; these can take up sub- stantial amounts of disk space. The default is /tmp. • NIX_REMOTE <#env-NIX_REMOTE> This variable should be set to daemon if you want to use the Nix daemon to execute Nix operations. This is necessary in multi-user Nix installations <../installation/multi-user.md>. If the Nix dae- mon's Unix socket is at some non-standard path, this variable should be set to unix://path/to/socket. Otherwise, it should be left unset. • NIX_SHOW_STATS <#env-NIX_SHOW_STATS> If set to 1, Nix will print some evaluation statistics, such as the number of values allocated. • NIX_COUNT_CALLS <#env-NIX_COUNT_CALLS> If set to 1, Nix will print how often functions were called during Nix expression evaluation. This is useful for profiling your Nix ex- pressions. • GC_INITIAL_HEAP_SIZE <#env-GC_INITIAL_HEAP_SIZE> If Nix has been configured to use the Boehm garbage collector, this variable sets the initial size of the heap in bytes. It defaults to 384 MiB. Setting it to a low value reduces memory consumption, but will increase runtime due to the overhead of garbage collection. XDG Base Directories Nix follows the XDG Base Directory Specification <https://specifica- tions.freedesktop.org/basedir-spec/basedir-spec-latest.html>. For backwards compatibility, Nix commands will follow the standard only when use-xdg-base-directories <../command-ref/conf-file.md#conf-use- xdg-base-directories> is enabled. New Nix commands <../command- ref/new-cli/nix.md> (experimental) conform to the standard by default. The following environment variables are used to determine locations of various state and configuration files: • [XDG_CONFIG_HOME]{#env-XDGCONFIGHOME} (default ~/.config) • [XDG_STATE_HOME]{#env-XDGSTATEHOME} (default ~/.local/state) • [XDG_CACHE_HOME]{#env-XDGCACHEHOME} (default ~/.cache) In addition, setting the following environment variables overrides the XDG base directories: • [NIX_CONFIG_HOME]{#env-NIXCONFIGHOME} (default $XDG_CONFIG_HOME/nix) • [NIX_STATE_HOME]{#env-NIXSTATEHOME} (default $XDG_STATE_HOME/nix) • [NIX_CACHE_HOME]{#env-NIXCACHEHOME} (default $XDG_CACHE_HOME/nix) When use-xdg-base-directories <../command-ref/conf-file.md#conf-use- xdg-base-directories> is enabled, the configuration directory is: 1. $NIX_CONFIG_HOME, if it is defined 2. Otherwise, $XDG_CONFIG_HOME/nix, if XDG_CONFIG_HOME is defined 3. Otherwise, ~/.config/nix. Likewise for the state and cache directories. Examples To build the dependencies of the package Pan, and start an interactive shell in which to build it: $ nix-shell '<nixpkgs>' --attr pan [nix-shell]$ eval ${unpackPhase:-unpackPhase} [nix-shell]$ cd $sourceRoot [nix-shell]$ eval ${patchPhase:-patchPhase} [nix-shell]$ 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 `config- urePhase', if it exists as a variable, otherwise evaluate the config- urePhase function. To clear the environment first, and do some additional automatic ini- tialisation of the interactive shell: $ nix-shell '<nixpkgs>' --attr 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 --expr 'with import <nixpkgs> { }; runCommand "dummy" { buildInputs = [ sqlite xorg.libX11 ]; } ""' A shorter way to do the same is: $ nix-shell --packages 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 --packages 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 Nix- pkgs: $ nix-shell --packages 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 --packages packages where real-interpreter is the real script interpreter that will be in- voked by nix-shell after it has obtained the dependencies and ini- tialised 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 python3 --packages python3 python3Packages.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 re- quires Perl and the HTML::TokeParser::Simple, LWP and LWP::Proto- col::Https packages: #! /usr/bin/env nix-shell #! nix-shell -i perl #! nix-shell --packages perl #! nix-shell --packages perlPackages.HTMLTokeParserSimple #! nix-shell --packages perlPackages.LWP #! nix-shell --packages perlPackages.LWPProtocolHttps use HTML::TokeParser::Simple; # Fetch nixos.org and print all hrefs. my $p = HTML::TokeParser::Simple->new(url => 'https://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 pack- age like Terraform: #! /usr/bin/env nix-shell #! nix-shell -i bash --packages 'terraform.withPlugins (plugins: [ plugins.openstack ])' terraform apply Note You must use single or double quotes (', ") when passing a sim- ple 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 sta- ble branch): #! /usr/bin/env nix-shell #! nix-shell -i runghc --packages '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 revi- sion 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 exam- ple, 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 con- tains: with import <nixpkgs> {}; runCommand "dummy" { buildInputs = [ python3 python3Packages.prettytable ]; } "" The script's file name is passed as the first argument to the inter- preter specified by the -i flag. Aside from the very first line, which is a directive to the operating system, the additional #! nix-shell lines do not need to be at the be- ginning of the file. This allows wrapping them in block comments for languages where # does not start a comment, such as ECMAScript, Erlang, PHP, or Ruby. nix-shell(1)
Name | Synopsis | Disambiguation | Description | Options | Common Options | Environment variables | Common Environment Variables | Examples
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