I am using OSX and I have pip installed for both Python3.5 and Python2.7. I know I can run the command pip2 to use Python2 and when I use the command pip3
Since you have specified in the comments you want syntax like pip install [package] to work, here is a solution:
Install setuptools for Python3: apt-get install python3-setuptools
Now pip for Python3 could be installed by: python3 -m easy_install pip
Now you can use pip with the specific version of Python to
install package for Python 3 by: pip-3.2 install [package]