go/src/cmd/dist/exec.go

// setDir sets cmd.Dir to dir, and also adds PWD=dir to cmd's environment.
func setDir(cmd *exec.Cmd, dir string) { … }

// setEnv sets cmd.Env so that key = value.
func setEnv(cmd *exec.Cmd, key, value string) { … }

// unsetEnv sets cmd.Env so that key is not present in the environment.
func unsetEnv(cmd *exec.Cmd, key string) { … }