---
name: "nix3-repl"
section: "1"
platform: "linux"
package: "nix-bin"
version: "2.26.3+dfsg-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/nix3-repl"
---

# 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.