Is there a script for downloading videos from YouTube utilising only Wget or curl on iPhone? I'm looking for a script that does not utilise youtube-dl and instead Wget or curl (coupled with things like sed and other base UNIX utilities that I wouldn't need to install, like no perl).

I'm asking for such a hassle of a job, as my iPhone running iOS 9 can't run utilities like Python or youtube-dl because of architecture issues.
No, there is not, because YouTube is desperate to prevent people from downloading their videos, and if it was that easy, too many people would do it.

youtube-dl has to be regularly updated to deal with the changes that YouTube and other sites implement to keep people from downloading videos.