# Command-line usage

## Invocation

Nox is normally invoked on the command line:

    nox

You can also invoke Nox via the Python interpreter:

    python3 -m nox

## Listing available sessions

To list all available sessions, including parametrized sessions:

    nox -l
    nox --list
    nox --list-sessions

## Running all sessions

You can run every session by just executing `nox` without any arguments:

    nox

The order that sessions are executed is the order that they appear in the Noxfile.

## Specifying one or more sessions

By default Nox will run all sessions defined in the noxfile. However, you can choose to run a particular set of them using `--session`, `-s`, or `-e`:

    nox --session tests
    nox -s lint tests
    nox -e lint

You can also use the `NOXSESSION` environment variable:

    NOXSESSION=lint nox
    NOXSESSION=lint,tests nox

Nox will run these sessions in the same order they are specified.

If you have a configured session’s virtualenv, you can choose to run only sessions with given Python versions:

    nox --python 3.8
    nox -p 3.7 3.8

You can also use pytest-style keywords to filter test sessions:

    nox -k "not lint"
    nox -k "tests and not lint"

## Specifying parametrized sessions

If you have a parametrized session such as:

    @nox.parametrize('django', ['1.9', '2.0'])
    def tests(session, django):
        ...

Then running `nox --session tests` will actually run all parametrized versions of the session. If you want the run the session with a particular set of parametrized arguments, you can specify them with the session name:

    nox --session "tests(django='1.9')"
    nox --session "tests(django='2.0')"

## Changing the sessions default backend

By default nox uses `virtualenv` as the virtual environment backend for the sessions, but it also supports `conda`, `mamba`, and `venv` as well as no backend (passthrough to whatever python environment nox is running on). You can change the default behaviour by using `-db <backend>` or `--default-venv-backend <backend>`. Supported names are `('none', 'virtualenv', 'conda', 'mamba', 'venv')`.

    nox -db conda
    nox --default-venv-backend conda

You can also set this option in the Noxfile with `nox.options.default_venv_backend`. In case both are provided, the commandline argument takes precedence.

Note that using this option does not change the backend for sessions where `venv_backend` is explicitly set.

## Forcing the sessions backend

You might work in a different environment than a project’s default continuous integration settings, and might wish to get a quick way to execute the same tasks but on a different venv backend. For this purpose, you can temporarily force the backend used by all sessions in the current nox execution by using `-fb <backend>` or `--force-venv-backend <backend>`. No exceptions are made, the backend will be forced for all sessions run whatever the other options values and nox file configuration. Supported names are `('none', 'virtualenv', 'conda', 'venv')`.

    nox -fb conda
    nox --force-venv-backend conda

You can also set this option in the Noxfile with `nox.options.force_venv_backend`. In case both are provided, the commandline argument takes precedence.

Finally note that the `--no-venv` flag is a shortcut for `--force-venv-backend none` and allows to temporarily run all selected sessions on the current python interpreter (the one running nox).

    nox --no-venv

## Re-using virtualenvs

By default, Nox deletes and recreates virtualenvs every time it is run. This is usually fine for most projects and continuous integration environments as pip’s caching makes re-install rather quick. However, there are some situations where it is advantageous to re-use the virtualenvs between runs. Use `-r` or `--reuse-existing-virtualenvs`:

    nox -r
    nox --reuse-existing-virtualenvs

If the Noxfile sets `nox.options.reuse_existing_virtualenvs`, you can override the Noxfile setting from the command line by using `--no-reuse-existing-virtualenvs`.

Additionally, you can skip the re-installation of packages when a virtualenv is reused. Use `-R` or `--reuse-existing-virtualenvs --no-install`:

    nox -R
    nox --reuse-existing-virtualenvs --no-install

The `--no-install` option causes the following session methods to return early:

- `session.install`

- `session.conda_install`

- `session.run_always`

This option has no effect if the virtualenv is not being reused.

## Running additional Python versions

In addition to Nox supporting executing single sessions, it also supports running Python versions that aren’t specified using `--extra-pythons`.

    nox --extra-pythons 3.8 3.9

This will, in addition to specified Python versions in the Noxfile, also create sessions for the specified versions.

This option can be combined with `--python` to replace, instead of appending, the Python interpreter for a given session:

    nox --python 3.10 --extra-python 3.10 -s lint

Instead of passing both options, you can use the `--force-python` shorthand:

    nox --force-python 3.10 -s lint

Also, you can specify `python` in place of a specific version. This will run the session using the `python` specified for the current `PATH`:

    nox --force-python python -s lint

## Stopping if any session fails

By default nox will continue to run all sessions even if one fails. You can use `--stop-on-first-error` to make nox abort as soon as the first session fails:

    nox --stop-on-first-error

If the Noxfile sets `nox.options.stop_on_first_error`, you can override the Noxfile setting from the command line by using `--no-stop-on-first-error`.

## Failing sessions when the interpreter is missing

By default, Nox will skip sessions where the Python interpreter can’t be found. If you want Nox to mark these sessions as failed, you can use `--error-on-missing-interpreters`:

    nox --error-on-missing-interpreters

If the Noxfile sets `nox.options.error_on_missing_interpreters`, you can override the Noxfile setting from the command line by using `--no-error-on-missing-interpreters`.

## Disallowing external programs

By default Nox will warn but ultimately allow you to run programs not installed in the session’s virtualenv. You can use `--error-on-external-run` to make Nox fail the session if it uses any external program without explicitly passing `external=True` into `session.run`:

    nox --error-on-external-run

If the Noxfile sets `nox.options.error_on_external_run`, you can override the Noxfile setting from the command line by using `--no-error-on-external-run`.

## Specifying a different configuration file

If for some reason your noxfile is not named noxfile.py, you can use `--noxfile` or `-f`:

    nox --noxfile something.py
    nox -f something.py

## Storing virtualenvs in a different directory

By default nox stores virtualenvs in `./.nox`, however, you can change this using `--envdir`:

    nox --envdir /tmp/envs

## Skipping everything but install commands

There are a couple of cases where it makes sense to have Nox only run `install` commands, such as preparing an environment for offline testing or re-creating the same virtualenvs used for testing. You can use `--install-only` to skip `run` commands.

For example, given this Noxfile:

    @nox.session
    def tests(session):
        session.install("pytest")
        session.install(".")
        session.run("pytest")

Running:

    nox --install-only

Would run both `install` commands, but skip the `run` command:

    nox > Running session tests
    nox > Creating virtualenv using python3.7 in ./.nox/tests
    nox > python -m pip install pytest
    nox > python -m pip install .
    nox > Skipping pytest run, as --install-only is set.
    nox > Session tests was successful.

## Forcing non-interactive behavior

`session.interactive` can be used to tell if Nox is being run from an interactive terminal (such as an actual human running it on their computer) vs run in a non-interactive terminal (such as a continuous integration system).

    @nox.session
    def docs(session):
        ...

        if session.interactive:
            nox.run("sphinx-autobuild", ...)
        else:
            nox.run("sphinx-build", ...)

Sometimes it’s useful to force Nox to see the session as non-interactive. You can use the `--non-interactive` argument to do this:

    nox --non-interactive

This will cause `session.interactive` to always return `False`.

## Controlling color output

By default, Nox will output colorful logs if you’re using in an interactive terminal. However, if you are redirecting `stderr` to a file or otherwise not using an interactive terminal, or the environment variable `NO_COLOR` is set, nox will output in plaintext. If this is not set, and `FORCE_COLOR` is present, color will be forced.

You can manually control Nox’s output using the `--nocolor` and `--forcecolor` flags.

For example, this will always output colorful logs:

    nox --forcecolor

However, this will never output colorful logs:

    nox --nocolor

## Controlling commands verbosity

By default, Nox will only show output of commands that fail, or, when the commands get passed `silent=False`. By passing `--verbose` to Nox, all output of all commands run is shown, regardless of the silent argument.

## Outputting a machine-readable report

You can output a report in `json` format by specifying `--report`:

    nox --report status.json

## Converting from tox

Nox has experimental support for converting `tox.ini` files into `noxfile.py` files. This doesn’t support every feature of tox and is intended to just do most of the mechanical work of converting over- you’ll likely still need to make a few changes to the converted `noxfile.py`.

To use the converter, install `nox` with the `tox_to_nox` extra:

    pip install --upgrade nox[tox_to_nox]

Then, just run `tox-to-nox` in the directory where your `tox.ini` resides:

    tox-to-nox

This will create a `noxfile.py` based on the environments in your `tox.ini`. Some things to note:

- Generative environments work, but will be converted as individual environments. `tox-to-nox` isn’t quite smart enough to turn these into parametrized sessions, but it should be straightforward to manually pull out common configuration for parametrization.

- Due to the way tox parses its configuration, all substitutions are baked in when converting. This means you’ll need to replace the static strings in the `noxfile.py` with appropriate variables.

- Several non-common tox options aren’t implemented, but it’s possible to do so. Please file a feature request if you run into one you think will be useful.

## Shell Completion

Add the appropriate command to your shell’s config file so that it is run on startup. You will likely have to restart or re-login for the autocompletion to start working.

bash

    eval "$(register-python-argcomplete nox)"

zsh

    # To activate completions for zsh you need to have
    # bashcompinit enabled in zsh:
    autoload -U bashcompinit
    bashcompinit

    # Afterwards you can enable completion for nox:
    eval "$(register-python-argcomplete nox)"

tcsh

    eval `register-python-argcomplete --shell tcsh nox`

fish

    register-python-argcomplete --shell fish nox | .