Yes, one should avoid reading what one did not write, or read very critically!
One shell / O/S I wandered onto had ksh set to nounset => reject reading nonexistent variables. None of my scripts worked! I had to turn that off quick in my .profile ! Talk about well know defaults, isn't "${some_name_never_set}" well known to be "" ?
It makes code more maintainable to not rely on defaults unless they are well known. For a boolean, you might use set and unset, and skip the content entirely.
---------- Post updated at 03:51 PM ---------- Previous update was at 03:50 PM ----------
AIX writes their own ksh?