Outside virtual environment

Run global pip (probably uses Python 2).

$ pip

Run global pip for Python 3.

$ pip3

Or

$ python3 -m pip

Or target a more specific version which is not your system default.

$ python3.8 -m pip

Upgrade pip. If you get permissions errors, as --user flag.

$ PIP_REQUIRE_VIRTUALENV pip install --upgrade pip
# OR
$ PIP_REQUIRE_VIRTUALENV python3 -m pip install --upgrade pip

Within a virtual environment

Run the pip which is in the scope of the environment - this requires the environment to be activated.

$ source venv/bin/activate
$ pip

Even if using Python 3, you won’t need to use pip3 - using pip in a virtual environment is fine.

This approach does not require the activate step.

$ venv/bin/pip