In Git and Subversion, how do I find out the current user at the terminal?

Presumably you are after the git user name that will be attached to any commits:

$ git config user.name
Wilbert Wilbert

$ git config --list
user.name=Wilbert Wilbert
user.email=wilbertwilbert@gmale.com
color.status=auto
color.branch=auto
...

Keys might appear more than once because Git reads from several files (/etc/gitconfig and ~/.gitconfig, for example). Git uses the last value for each key it sees.