nix3-repl - Man Page

start an interactive environment for evaluating Nix expressions

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

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 is read from standard input. Implies --impure.
Note
See man nix.conf for overriding configuration settings with command line flags.