Meltano

I'm going to start digging into the code, but it looks like meltano install does not honor the PIP_INDEX_URL environment variable.  Most likely I can create a ~/.config/pip/pip.conf, but it would be nice if the env var was honored.  Anyone know?

We use the env var during our installation process and it seems to work fine. It’s also mentioned in the docs <https://meltano.com/docs/plugin-management.html#installing-plugins-from-a-custom-python-package-index-pypi|here>

That is exactly what I'm doing:
```export PIP_INDEX_URL=https://....
meltano install```
That does not work.  If I run pip install instead it works fine.

It was working before.  I think, for some reason, you need to include pip_url in your meltano.yaml file for it to work.  I didn't figure I'd need it, since it should be able to find it, but apparently it is required.  Not sure it should be failing if it is not included.  I'm not specifying the full name, but just a `pip_url: tap-name==version` appears to make it work..

<@U06CBPBGMGT>
&gt; Not sure it should be failing if it is not included
Plugins can work with only an arbitrary `executable` that you install/include by means other than pip. If the plugin is a Python package that you expect to be installed, you do need to define a `pip_url` which can be any valid <https://pip.pypa.io/en/stable/cli/pip_install/#requirement-specifiers|requirement specifier>: PyPI (or a private repo) version, git url, local path, etc.

Gotcha.  I had assumed that it would default to the name of the loader, but thanks for the feedback.