Never used these and have no clue what they do or what purpose they serve: ... flock ...

While I doubt you'll see a separate response for each function in your long list, I'm delighted to provide a response for flock:

• Ensure only one copy of a script runs at a time ... using flock - I've used this handy and simple trick quite a few times over the years
• my @chickens by pjf - flock features in this classic Perl poem (rated fourth best at The Top Ten Perl Poems)