virtualenv is primarily a command line application.
It modifies the environment variables in a shell to create an isolated Python environment, so you'll need to have a
shell to run it. You can type in
virtualenv (name of the application) followed by flags that control its
behaviour. All options have sensible defaults, and there's one required argument: then name/path of the virtual
environment to create. The default values for the command line options can be overridden via the
:ref:`conf_file` or :ref:`env_vars`. Environment variables takes priority over the configuration file values
--help will show if a default comes from the environment variable as the help message will end in this case
with environment variables or the configuration file).
The options that can be passed to virtualenv, along with their default values and a short description are listed below.
.. table_cli:: :module: virtualenv.run :func: build_parser
virtualenv looks for a standard ini configuration file. The exact location depends on the operating system you're using,
as determined by :pypi:`appdirs` application data definition. The configuration file location is printed as at the end of
the output when
--help is passed.
The keys of the settings are derived from the long command line option. For example, :option:`--python <python>` would be specified as:
[virtualenv] python = /opt/python-3.3/bin/python
Options that take multiple values, like :option:`extra-search-dir` can be specified as:
[virtualenv] extra-search-dir = /path/to/dists /path/to/other/dists
Each command line option has a corresponding environment variables with the name format
UPPER_NAME is the name of the command line options capitalized and
'-') replaced with underscores (
For example, to use a custom Python binary, instead of the one virtualenv is run with, you can set the environment
env VIRTUALENV_PYTHON=/opt/python-3.8/bin/python virtualenv
This also works for appending command line options, like :option:`extra-search-dir`, where a literal newline is used to separate the values:
env VIRTUALENV_EXTRA_SEARCH_DIR="/path/to/dists\n/path/to/other/dists" virtualenv
The equivalent CLI-flags based invocation, for the above example, would be:
virtualenv --extra-search-dir=/path/to/dists --extra-search-dir=/path/to/other/dists