Technical Notes

Manpages - nix3-repl.1

Warning
This program is experimental and its interface is subject to change.

#+end_quote

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.