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CLI interface

CLI flags

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 conf_file or 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.

virtualenv [OPTIONS]

Defaults

Configuration file

virtualenv looks for a standard ini configuration file. The exact location depends on the operating system you're using, as determined by platformdirs application configuration 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 command line option (left strip the - characters, and replace - with _). Where multiple flags are available first found wins (where order is as it shows up under the --help).

For example, --python <python> would be specified as:

[virtualenv]
python = /opt/python-3.8/bin/python

Options that take multiple values, like extra-search-dir can be specified as:

[virtualenv]
extra_search_dir =
    /path/to/dists
    /path/to/other/dists

Environment Variables

Default values may be also specified via environment variables. The keys of the settings are derived from the command line option (left strip the - characters, and replace - with _, finally capitalize the name). Where multiple flags are available first found wins (where order is as it shows up under the --help).

For example, to use a custom Python binary, instead of the one virtualenv is run with, you can set the environment variable VIRTUALENV_PYTHON like:

env VIRTUALENV_PYTHON=/opt/python-3.8/bin/python virtualenv

Where the option accepts multiple values, for example for python or extra-search-dir, the values can be separated either by literal newlines or commas. Newlines and commas can not be mixed and if both are present only the newline is used for separating values. Examples for multiple values:

env VIRTUALENV_PYTHON=/opt/python-3.8/bin/python,python3.8 virtualenv
env VIRTUALENV_EXTRA_SEARCH_DIR=/path/to/dists\n/path/to/other/dists virtualenv

The equivalent CLI-flags based invocation for the above examples would be:

virtualenv --python=/opt/python-3.8/bin/python --python=python3.8
virtualenv --extra-search-dir=/path/to/dists --extra-search-dir=/path/to/other/dists