The shell will default to using the built-in, if it has one and you have not explicitly specified the external one.
There's no way to tell 'at a glance' but you could read the man pages/web eg
and you could use the 'find' cmd to see if there's an external (aka standalone) version of any cmd.
A similar case (this is actually to do with the PATH env var) is in crontab entries.
The cron daemon has a minimal env, so if you call a cmd that is not built-in, it will most likely not work unless:
1. you specify the complete/absolute path eg
2. you have exported the cmd path into the env for your script.