$ gsutil version -l
[...]
using cloud sdk: True
config path(s): /home/USER/.boto, /home/USER/.config/gcloud/legacy_credentials/USER@gmail.com/.boto
[...]

if [ -d "/path/to/standalone/gsutil/directory" ]; then
  PATH="/path/to/standalone/gsutil/directory:$PATH"
fi

$ source "$HOME/.bashrc"; gsutil version -l

$ type gsutil

$ gsutil config