> as a self-respecting software engineer
Then you probably already know more about C than you realise: if, while, for, etc. all work the same as most other languages.
What you're probably not used to is needing to define functions in advance, pointers, and memory (de)allocation.
If you learn by doing, then with google and github, you can create a few simplified versions of unix utilities (cat, ls, grep -F).
If you're on Windows, I recommend using a Linux VM, WSL, or Cygwin - it's easier to setup than the C tooling in Windows (and you're stealth learning something else).
Once you know C, you can then move onto C++ (I stopped at C).
Agreed. APUE is perhaps one of the best book available covering SUS, POSIX layer in detail.
Nice. I'll check it out.