Reference

nix3-repl(1)

start an interactive environment for evaluating Nix expressions

Warning
This program is experimental ⟨@docroot@/development/experimental-features.md#xp-feature-nix-command⟩ and its interface is subject to change.

Name

nix repl - start an interactive environment for evaluating Nix expressions

Synopsis

nix repl [option…] installables…

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> :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

•

--stdin ⟨#opt-stdin⟩

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

Common evaluation options

•

--arg ⟨#opt-arg⟩ name expr

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

•

--arg-from-file ⟨#opt-arg-from-file⟩ name path

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

•

--arg-from-stdin ⟨#opt-arg-from-stdin⟩ name

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

•

--argstr ⟨#opt-argstr⟩ name string

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

•

--debugger ⟨#opt-debugger⟩

Start an interactive environment if evaluation fails.

•

--eval-store ⟨#opt-eval-store⟩ store-url

The URL of the Nix store ⟨@docroot@/store/types/index.md#store-url-format⟩ to use for evaluation, i.e. to store derivations (.drv files) and inputs referenced by them.

•

--impure ⟨#opt-impure⟩

Allow access to mutable paths and repositories.

•

--include ⟨#opt-include⟩ / -I path

Add path to search path entries used to resolve lookup paths ⟨@docroot@/language/constructs/lookup-path.md⟩

This option may be given multiple times.

Paths added through -I take precedence over the nix-path configuration setting ⟨@docroot@/command-ref/conf-file.md#conf-nix-path⟩ and the NIX_PATH environment variable ⟨@docroot@/command-ref/env-common.md#env-NIX_PATH⟩\c .

•

--override-flake ⟨#opt-override-flake⟩ original-ref resolved-ref

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

Common flake-related options

•

--commit-lock-file ⟨#opt-commit-lock-file⟩

Commit changes to the flake’s lock file.

•

--inputs-from ⟨#opt-inputs-from⟩ flake-url

Use the inputs of the specified flake as registry entries.

•

--no-registries ⟨#opt-no-registries⟩

Don’t allow lookups in the flake registries.

DEPRECATED

Use --no-use-registries ⟨@docroot@/command-ref/conf-file.md#conf-use-registries⟩ instead.

•

--no-update-lock-file ⟨#opt-no-update-lock-file⟩

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

•

--no-write-lock-file ⟨#opt-no-write-lock-file⟩

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

•

--output-lock-file ⟨#opt-output-lock-file⟩ flake-lock-path

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

•

--override-input ⟨#opt-override-input⟩ input-path flake-url

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

•

--recreate-lock-file ⟨#opt-recreate-lock-file⟩

Recreate the flake’s lock file from scratch.

DEPRECATED

Use nix flake update ⟨@docroot@/command-ref/new-cli/nix3-flake-update.md⟩ instead.

•

--reference-lock-file ⟨#opt-reference-lock-file⟩ flake-lock-path

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

•

--update-input ⟨#opt-update-input⟩ input-path

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

DEPRECATED

Use nix flake update ⟨@docroot@/command-ref/new-cli/nix3-flake-update.md⟩ instead.

Logging-related options

•

--debug ⟨#opt-debug⟩

Set the logging verbosity level to ‘debug’.

•

--log-format ⟨#opt-log-format⟩ format

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

•

--print-build-logs ⟨#opt-print-build-logs⟩ / -L

Print full build logs on standard error.

•

--quiet ⟨#opt-quiet⟩

Decrease the logging verbosity level.

•

--verbose ⟨#opt-verbose⟩ / -v

Increase the logging verbosity level.

Miscellaneous global options

•

--help ⟨#opt-help⟩

Show usage information.

•

--offline ⟨#opt-offline⟩

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

•

--option ⟨#opt-option⟩ name value

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

•

--refresh ⟨#opt-refresh⟩

Consider all previously downloaded files out-of-date.

•

--repair ⟨#opt-repair⟩

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

•

--version ⟨#opt-version⟩

Show version information.

Options that change the interpretation of installables

•

--expr ⟨#opt-expr⟩ expr

Interpret installables ⟨@docroot@/command-ref/new-cli/nix.md#installables⟩ as attribute paths relative to the Nix expression expr.

•

--file ⟨#opt-file⟩ / -f file

Interpret installables ⟨@docroot@/command-ref/new-cli/nix.md#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 ⟨@docroot@/command-ref/conf-file.md#command-line-flags⟩ for overriding configuration settings with command line flags.

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