> that leaves shell-integration scripts: virtualenv, rbenv, etc. Supporting that stuff is one of the most common requests that the fish shell gets, and one of the most commonly cited reasons for not using fish.

shameless plug, but I made a utility to solve the problem: https://github.com/edc/bass

So you can write `bass source /usr/local/bin/virtualenvwrapper.sh ';' mkvirtualenv env1`, which of course can be shortened with a function.