auto_envvar_prefix does not work with command groups

[BlinkyStitt]

I made this example program:

import click


@click.group()
@click.option('--debug/--no-debug')
def cli(debug):
    click.echo('Debug mode is %s' % ('on' if debug else 'off'))


@cli.command()
@click.option('--username')
def greet(username):
    click.echo('Hello %s!' % username)


if __name__ == '__main__':
    cli(auto_envvar_prefix='GREETER')

auto_envvar_prefix only works for GREETER_DEBUG. Setting GREETER_USERNAME has no effect

Expected result:

$ export GREETER_DEBUG="false"
$ export GREETER_USERNAME="John"
$ python greet.py greet
Debug mode is off
Hello John!

Actual result:

$ export GREETER_DEBUG="false"
$ export GREETER_USERNAME="John"
$ python greet.py greet
Debug mode is off
Hello None!

For now, I am setting envvar on my options, but there are a lot of them

[ptpt]

Try GREETER_GREET_USERNAME.

[vlcinsky]

The @ptpt advice works, setting option values via env vars requires not only prefix, but also group name to be present.

It would be great to have such information as example in doc.