Sorry, my bad. $GOPATH is the Unix shell syntax for the value of environment variable GOPATH. If you use Windows, the syntax would be %GOPATH% instead. Here, I used the syntax only as a shortcut for “the directory that your GOPATH points to”. I realize now that this was too sloppy. Moreover, the $GOPATH environment variable may not even exist on your system. (It is optional since Go 1.8.) The command go env GOPATH is the authoritative way of determining the current value of the GOPATH.
And yes, the go commands require a terminal.