Warning
This program is experimental and its interface is subject to change.
Name
nix repl - start an interactive environment for evaluating Nix expressions
Synopsis
nix repl [option...] installables...
Note: this command's interface is based heavily around installables, which you may want to read about first (nix --help).
Examples
-
Display all special commands within the REPL:
# nix repl nix-repl> :? -
Evaluate some simple Nix expressions:
# nix repl nix-repl> 1 + 2 3 nix-repl> map (x: x * 2) [1 2 3] [ 2 4 6 ] -
Interact with Nixpkgs in the REPL:
# nix repl --file example.nix Loading Installable ''... Added 3 variables. # nix repl --expr '{a={b=3;c=4;};}' Loading Installable ''... Added 1 variables. # nix repl --expr '{a={b=3;c=4;};}' a Loading Installable ''... Added 1 variables. # nix repl --extra-experimental-features 'flakes' nixpkgs Loading Installable 'flake:nixpkgs#'... Added 5 variables. nix-repl> legacyPackages.x86_64-linux.emacs.name "emacs-27.1" nix-repl> legacyPackages.x86_64-linux.emacs.name "emacs-27.1" nix-repl> :q # nix repl --expr 'import <nixpkgs>{}' Loading Installable ''... Added 12439 variables. nix-repl> emacs.name "emacs-27.1" nix-repl> emacs.drvPath "/nix/store/lp0sjrhgg03y2n0l10n70rg0k7hhyz0l-emacs-27.1.drv" nix-repl> drv = runCommand "hello" { buildInputs = [ hello ]; } "hello; hello > $out" nix-repl> :b drv this derivation produced the following outputs: out -> /nix/store/0njwbgwmkwls0w5dv9mpc1pq5fj39q0l-hello nix-repl> builtins.readFile drv "Hello, world!\n" nix-repl> :log drv Hello, world!
Description
This command provides an interactive environment for evaluating Nix expressions. (REPL stands for 'read–eval–print loop'.)
On startup, it loads the Nix expressions named files and adds them
into the lexical scope. You can load addition files using the :l <filename> command, or reload all files using :r.
Options
--stdinRead installables from the standard input. No default installable applied.
Common evaluation options:
-
--argname expr Pass the value expr as the argument name to Nix functions. -
--argstrname string Pass the string string as the argument name to Nix functions. -
--debuggerStart an interactive environment if evaluation fails. -
--eval-storestore-url The URL of the Nix store to use for evaluation, i.e. to store derivations (.drvfiles) and inputs referenced by them. -
--impureAllow access to mutable paths and repositories. -
--include/-Ipath Add path to the Nix search path. The Nix search path is initialized from the colon-separatedNIX_PATHenvironment 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/nixoswill cause Lix to look for paths relative to
/home/eelco/Devand/etc/nixos, in that order. This is equivalent to setting theNIX_PATHenvironment variable to/home/eelco/Dev:/etc/nixosIt is also possible to match paths against a prefix. For example, passing
-I nixpkgs=/home/eelco/Dev/nixpkgs-branch -I /etc/nixoswill cause Lix to search for
<nixpkgs/path>in/home/eelco/Dev/nixpkgs-branch/pathand/etc/nixos/nixpkgs/path.If a path in the Nix search path starts with
http://orhttps://, 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.gztells Lix to download and use the current contents of the
masterbranch in thenixpkgsrepository.The URLs of the tarballs from the official
nixos.orgchannels (see the manual page fornix-channel) can be abbreviated aschannel:<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.xzYou can also fetch source trees using flake URLs and add them to the search path. For instance,
-I nixpkgs=flake:nixpkgsspecifies that the prefix
nixpkgsshall refer to the source tree downloaded from thenixpkgsentry in the flake registry. Similarly,-I nixpkgs=flake:github:NixOS/nixpkgs/nixos-22.05makes
<nixpkgs>refer to a particular branch of theNixOS/nixpkgsrepository on GitHub. -
--override-flakeoriginal-ref resolved-ref Override the flake registries, redirecting original-ref to resolved-ref.
Common flake-related options:
-
--commit-lock-fileCommit changes to the flake's lock file. -
--inputs-fromflake-url Use the inputs of the specified flake as registry entries. -
--no-registriesDon't allow lookups in the flake registries. This option is deprecated; use--no-use-registries. -
--no-update-lock-fileDo not allow any updates to the flake's lock file. -
--no-write-lock-fileDo not write the flake's newly generated lock file. -
--output-lock-fileflake-lock-path Write the given lock file instead offlake.lockwithin the top-level flake. -
--override-inputinput-path flake-url Override a specific flake input (e.g.dwarffs/nixpkgs). This implies--no-write-lock-file. -
--reference-lock-fileflake-lock-path Read the given lock file instead offlake.lockwithin the top-level flake.
Logging-related options:
-
--debugSet the logging verbosity level to 'debug'. -
--log-formatformat Set the format of log output; one ofraw,internal-json,bar,bar-with-logs,multilineormultiline-with-logs. -
--print-build-logs/-LPrint full build logs on standard error. -
--quietDecrease the logging verbosity level. -
--verbose/-vIncrease the logging verbosity level.
Miscellaneous global options:
-
--helpShow usage information. -
--offlineDisable substituters and consider all previously downloaded files up-to-date. -
--optionname value Set the Lix configuration setting name to value (overridingnix.conf). -
--refreshConsider all previously downloaded files out-of-date. -
--repairDuring evaluation, rewrite missing or corrupted files in the Nix store. During building, rebuild missing or corrupted store paths. -
--versionShow version information.
Options that change the interpretation of installables:
-
--expr/-Eexpr Interpret installables as attribute paths relative to the Nix expression expr. -
--file/-ffile 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.conffor overriding configuration settings with command line flags.