World's easiest question for anyone but me: Why is go get github.com/go-sql-driver/mysql failing?

Trying to use the go-sql-driver/mysql package. When I do this:

go get github.com/go-sql-driver/mysql

I get the error package github.com/go-sql-driver/mysql: cannot download, $GOPATH not set. For more details see: go help gopath

I have read https://golang.org/doc/code.html 72 times and seem to be missing something. Here's my config. (By the way, a "hello world" program works just fine.)

PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/go/bin:/usr/local/mysql/bin/:/bin
GOPATH=/Users/tom/go

The program named foo.go is in:

/Users/tom/go/foo

What am I doing wrong?

Are you missing an export GOPATHin your rc file?

You need to export GOPATH, otherwise go won't know the path. 

export GOPATH=<path>

or 

GOPATH=<path>
export GOPATH

This should go into your .bashrc and you need to reload it with source .bashrc

Where is your config set?

Your program needs to be in $GOPATH/src/foo/ (or more commonly $GOPATH/src/github.com/username/foo)