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...

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 repl-flake' 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

--stdin

Read installables from the standard input.

Common evaluation options:

--arg name expr

Pass the value expr as the argument name to Nix functions.
--argstr name string

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

Start an interactive environment if evaluation fails.
--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.
--impure

Allow access to mutable paths and repositories.
--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.
--override-flake original-ref resolved-ref

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

Common flake-related options:

--commit-lock-file

Commit changes to the flake's lock file.
--inputs-from flake-url

Use the inputs of the specified flake as registry entries.
--no-registries

Don't allow lookups in the flake registries. This option is deprecated; use --no-use-registries.
--no-update-lock-file

Do not allow any updates to the flake's lock file.
--no-write-lock-file

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

Write the given lock file instead of flake.lock within the top-level flake.
--override-input input-path flake-url

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

Recreate the flake's lock file from scratch.
--reference-lock-file flake-lock-path

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

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

Logging-related options:

--debug

Set the logging verbosity level to 'debug'.
--log-format format

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

Print full build logs on standard error.
--quiet

Decrease the logging verbosity level.
--verbose / -v

Increase the logging verbosity level.

Miscellaneous global options:

--help

Show usage information.
--offline

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

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

Consider all previously downloaded files out-of-date.
--version

Show version information.

Options that change the interpretation of installables:

--expr expr

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

Options to override configuration settings:

--accept-flake-config

Enable the accept-flake-config setting.
--access-tokens value

Set the access-tokens setting.
--allow-dirty

Enable the allow-dirty setting.
--allow-import-from-derivation

Enable the allow-import-from-derivation setting.
--allow-new-privileges

Enable the allow-new-privileges setting.
--allow-symlinked-store

Enable the allow-symlinked-store setting.
--allow-unsafe-native-code-during-evaluation

Enable the allow-unsafe-native-code-during-evaluation setting.
--allowed-impure-host-deps value

Set the allowed-impure-host-deps setting.
--allowed-uris value

Set the allowed-uris setting.
--allowed-users value

Set the allowed-users setting.
--auto-allocate-uids

Enable the auto-allocate-uids setting.
--auto-optimise-store

Enable the auto-optimise-store setting.
--bash-prompt value

Set the bash-prompt setting.
--bash-prompt-prefix value

Set the bash-prompt-prefix setting.
--bash-prompt-suffix value

Set the bash-prompt-suffix setting.
--build-hook value

Set the build-hook setting.
--build-poll-interval value

Set the build-poll-interval setting.
--build-users-group value

Set the build-users-group setting.
--builders value

Set the builders setting.
--builders-use-substitutes

Enable the builders-use-substitutes setting.
--commit-lockfile-summary value

Set the commit-lockfile-summary setting.
--compress-build-log

Enable the compress-build-log setting.
--connect-timeout value

Set the connect-timeout setting.
--cores value

Set the cores setting.
--diff-hook value

Set the diff-hook setting.
--download-attempts value

Set the download-attempts setting.
--download-speed value

Set the download-speed setting.
--eval-cache

Enable the eval-cache setting.
--experimental-features value

Set the experimental-features setting.
--extra-access-tokens value

Append to the access-tokens setting.
--extra-allowed-impure-host-deps value

Append to the allowed-impure-host-deps setting.
--extra-allowed-uris value

Append to the allowed-uris setting.
--extra-allowed-users value

Append to the allowed-users setting.
--extra-experimental-features value

Append to the experimental-features setting.
--extra-extra-platforms value

Append to the extra-platforms setting.
--extra-hashed-mirrors value

Append to the hashed-mirrors setting.
--extra-ignored-acls value

Append to the ignored-acls setting.
--extra-nix-path value

Append to the nix-path setting.
--extra-platforms value

Set the extra-platforms setting.
--extra-plugin-files value

Append to the plugin-files setting.
--extra-sandbox-paths value

Append to the sandbox-paths setting.
--extra-secret-key-files value

Append to the secret-key-files setting.
--extra-substituters value

Append to the substituters setting.
--extra-system-features value

Append to the system-features setting.
--extra-trusted-public-keys value

Append to the trusted-public-keys setting.
--extra-trusted-substituters value

Append to the trusted-substituters setting.
--extra-trusted-users value

Append to the trusted-users setting.
--fallback

Enable the fallback setting.
--filter-syscalls

Enable the filter-syscalls setting.
--flake-registry value

Set the flake-registry setting.
--fsync-metadata

Enable the fsync-metadata setting.
--gc-reserved-space value

Set the gc-reserved-space setting.
--hashed-mirrors value

Set the hashed-mirrors setting.
--http-connections value

Set the http-connections setting.
--http2

Enable the http2 setting.
--id-count value

Set the id-count setting.
--ignore-try

Enable the ignore-try setting.
--ignored-acls value

Set the ignored-acls setting.
--impersonate-linux-26

Enable the impersonate-linux-26 setting.
--keep-build-log

Enable the keep-build-log setting.
--keep-derivations

Enable the keep-derivations setting.
--keep-env-derivations

Enable the keep-env-derivations setting.
--keep-failed

Enable the keep-failed setting.
--keep-going

Enable the keep-going setting.
--keep-outputs

Enable the keep-outputs setting.
--log-lines value

Set the log-lines setting.
--max-build-log-size value

Set the max-build-log-size setting.
--max-free value

Set the max-free setting.
--max-jobs value

Set the max-jobs setting.
--max-silent-time value

Set the max-silent-time setting.
--min-free value

Set the min-free setting.
--min-free-check-interval value

Set the min-free-check-interval setting.
--nar-buffer-size value

Set the nar-buffer-size setting.
--narinfo-cache-negative-ttl value

Set the narinfo-cache-negative-ttl setting.
--narinfo-cache-positive-ttl value

Set the narinfo-cache-positive-ttl setting.
--netrc-file value

Set the netrc-file setting.
--nix-path value

Set the nix-path setting.
--no-accept-flake-config

Disable the accept-flake-config setting.
--no-allow-dirty

Disable the allow-dirty setting.
--no-allow-import-from-derivation

Disable the allow-import-from-derivation setting.
--no-allow-new-privileges

Disable the allow-new-privileges setting.
--no-allow-symlinked-store

Disable the allow-symlinked-store setting.
--no-allow-unsafe-native-code-during-evaluation

Disable the allow-unsafe-native-code-during-evaluation setting.
--no-auto-allocate-uids

Disable the auto-allocate-uids setting.
--no-auto-optimise-store

Disable the auto-optimise-store setting.
--no-builders-use-substitutes

Disable the builders-use-substitutes setting.
--no-compress-build-log

Disable the compress-build-log setting.
--no-eval-cache

Disable the eval-cache setting.
--no-fallback

Disable the fallback setting.
--no-filter-syscalls

Disable the filter-syscalls setting.
--no-fsync-metadata

Disable the fsync-metadata setting.
--no-http2

Disable the http2 setting.
--no-ignore-try

Disable the ignore-try setting.
--no-impersonate-linux-26

Disable the impersonate-linux-26 setting.
--no-keep-build-log

Disable the keep-build-log setting.
--no-keep-derivations

Disable the keep-derivations setting.
--no-keep-env-derivations

Disable the keep-env-derivations setting.
--no-keep-failed

Disable the keep-failed setting.
--no-keep-going

Disable the keep-going setting.
--no-keep-outputs

Disable the keep-outputs setting.
--no-preallocate-contents

Disable the preallocate-contents setting.
--no-print-missing

Disable the print-missing setting.
--no-pure-eval

Disable the pure-eval setting.
--no-require-sigs

Disable the require-sigs setting.
--no-restrict-eval

Disable the restrict-eval setting.
--no-run-diff-hook

Disable the run-diff-hook setting.
--no-sandbox

Disable sandboxing.
--no-sandbox-fallback

Disable the sandbox-fallback setting.
--no-show-trace

Disable the show-trace setting.
--no-substitute

Disable the substitute setting.
--no-sync-before-registering

Disable the sync-before-registering setting.
--no-trace-function-calls

Disable the trace-function-calls setting.
--no-trace-verbose

Disable the trace-verbose setting.
--no-use-case-hack

Disable the use-case-hack setting.
--no-use-cgroups

Disable the use-cgroups setting.
--no-use-registries

Disable the use-registries setting.
--no-use-sqlite-wal

Disable the use-sqlite-wal setting.
--no-use-xdg-base-directories

Disable the use-xdg-base-directories setting.
--no-warn-dirty

Disable the warn-dirty setting.
--plugin-files value

Set the plugin-files setting.
--post-build-hook value

Set the post-build-hook setting.
--pre-build-hook value

Set the pre-build-hook setting.
--preallocate-contents

Enable the preallocate-contents setting.
--print-missing

Enable the print-missing setting.
--pure-eval

Enable the pure-eval setting.
--relaxed-sandbox

Enable sandboxing, but allow builds to disable it.
--require-sigs

Enable the require-sigs setting.
--restrict-eval

Enable the restrict-eval setting.
--run-diff-hook

Enable the run-diff-hook setting.
--sandbox

Enable sandboxing.
--sandbox-build-dir value

Set the sandbox-build-dir setting.
--sandbox-dev-shm-size value

Set the sandbox-dev-shm-size setting.
--sandbox-fallback

Enable the sandbox-fallback setting.
--sandbox-paths value

Set the sandbox-paths setting.
--secret-key-files value

Set the secret-key-files setting.
--show-trace

Enable the show-trace setting.
--ssl-cert-file value

Set the ssl-cert-file setting.
--stalled-download-timeout value

Set the stalled-download-timeout setting.
--start-id value

Set the start-id setting.
--store value

Set the store setting.
--substitute

Enable the substitute setting.
--substituters value

Set the substituters setting.
--sync-before-registering

Enable the sync-before-registering setting.
--system value

Set the system setting.
--system-features value

Set the system-features setting.
--tarball-ttl value

Set the tarball-ttl setting.
--timeout value

Set the timeout setting.
--trace-function-calls

Enable the trace-function-calls setting.
--trace-verbose

Enable the trace-verbose setting.
--trusted-public-keys value

Set the trusted-public-keys setting.
--trusted-substituters value

Set the trusted-substituters setting.
--trusted-users value

Set the trusted-users setting.
--use-case-hack

Enable the use-case-hack setting.
--use-cgroups

Enable the use-cgroups setting.
--use-registries

Enable the use-registries setting.
--use-sqlite-wal

Enable the use-sqlite-wal setting.
--use-xdg-base-directories

Enable the use-xdg-base-directories setting.
--user-agent-suffix value

Set the user-agent-suffix setting.
--warn-dirty

Enable the warn-dirty setting.

Nix Reference Manual

Name

Synopsis

Examples

Description

Options