Executes the purge functionality.

def do_purge(bare=False, downloads=False, allow_global=False):
    """Executes the purge functionality."""

    if downloads:
        if not bare:
            click.echo(crayons.normal(fix_utf8("Clearing out downloads directory…"), bold=True))
        vistir.path.rmtree(project.download_location)
        return

    # Remove comments from the output, if any.
    installed = set([
        pep423_name(pkg.project_name) for pkg in project.environment.get_installed_packages()
    ])
    bad_pkgs = set([pep423_name(pkg) for pkg in BAD_PACKAGES])
    # Remove setuptools, pip, etc from targets for removal
    to_remove = installed - bad_pkgs

    # Skip purging if there is no packages which needs to be removed
    if not to_remove:
        if not bare:
            click.echo("Found 0 installed package, skip purging.")
            click.echo(crayons.green("Environment now purged and fresh!"))
        return installed

    if not bare:
        click.echo(
            fix_utf8("Found {0} installed package(s), purging…".format(len(to_remove)))
        )

    command = "{0} uninstall {1} -y".format(
        escape_grouped_arguments(which_pip(allow_global=allow_global)),
        " ".join(to_remove),
    )
    if environments.is_verbose():
        click.echo("$ {0}".format(command))
    c = delegator.run(command)
    if c.return_code != 0:
        raise exceptions.UninstallError(installed, command, c.out + c.err, c.return_code)
    if not bare:
        click.echo(crayons.blue(c.out))
        click.echo(crayons.green("Environment now purged and fresh!"))
    return installed