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

• --debugger
  start an interactive environment if evaluation fails

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.

• --eval-store store-url
  The Nix store to use for evaluations.

• --impure
  Allow access to mutable paths and repositories.

• --include / -I path
  Add path to the list of locations used to look up <...> file names.

• --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.

• --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.

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

Options that change the interpretation of installables:

• --derivation
  Operate on the store derivation rather than its outputs.

• --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.