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' 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

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

Common evaluation options

• --arg name expr

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

• --arg-from-file name path

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

• --arg-from-stdin name

  Pass the contents of stdin 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 search path entries used to resolve lookup paths

  This option may be given multiple times.

  Paths added through -I take precedence over the nix-path configuration setting and the NIX_PATH environment variable.

• --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.

  DEPRECATED

  Use --no-use-registries instead.

• --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.

  DEPRECATED

  Use nix flake update instead.

• --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).

  DEPRECATED

  Use nix flake update instead.

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.

• --repair

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

• --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.

Note

See man nix.conf for overriding configuration settings with command line flags.