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.

                                                                                                    nix3-repl(1)