Allow to install multiple packages

Edit Adjusted the title because there is another proposal not related to --spec option in https://github.com/pipxproject/pipx/issues/88#issuecomment-461373956

Instead of using inject to install optional dependencies or plugins, it would be much nicer just to pass --spec multiple times, e.g. pipx install flake8 --spec "flake8" --spec "flake8-print".

This makes inject obsolete and you should deprecate it. Instead of inject you should use upgrade with specs.

So in combination with #87 this gives you a very nice way to port your pipx venvs to another PC. Just copy your pipx config file and run reinstall-all. This would also fix #63.

This would somehow give a solution for #83, too. Instead of having a venv for every cmd he could install multiple commands in one “grouped” venv.

[schlamar]

Just one last addition (I hope): The main benefit is that you can install multiple packages at once with a single command. Doing pipx install flake8 + pipx inject flake8 flake8-print just to install two packages in a venv is not “nice”.

I thought this would be obvious but as @taketwo did not react to that advantage maybe it isn’t 😃

[schlamar]

Maybe better: allow packages separated by whitespace in spec so this would be equal to pip install and pipx inject:

pipx install flake8 --spec "flake8 flake8-print"