gofmt -w .   # formats files in current directory and all sub-directories
 go fmt ./... # similar to previous
 go fmt .     # formats files in current package
 gofmt -w foo/bar # formats files in directory $PWD/foo/bar and sub-dirs
 go fmt foo/bar   # formats files in directory $GOPATH/src/foo/bar
 gofmt -w     # error, no file or directory specified
 go fmt       # formats files in current package