I'm glad that my code helped, but there isn't anything overwhelming in what I did. Start at the beginning and decide what you want to do. Then build the pieces you need to get there one by one until you have something that works. If you run into a problem with one of the pieces fitting in after you have started working on another piece, don't be afraid to throw one or both of them away and redo it/them a different way that fits in better.

I have no idea what a regular CS graduate now days knows about C, nor how long it takes one to be able to read, understand, nor write a program like this. But, a few decades of fixing bugs in other people's code, writing my own code, and writing and maintaining the standards that specify the behavior of the POSIX-specified utilities and C interfaces certainly helps. The key point is that practicing programming helps.

When I was a CS grad, I knew FORTRAN and three different assembler languages and a couple of FORTRAN high precision math libraries. I picked up Algol, COBOL, Lisp, and PL/1 in a comparative programming languages course one semester while working on my Masters in computer engineering. (I used to have decks of cards in Algol, COBOL, Fortran, Lisp, and PL/1 that could read in a number expressed as Roman numerals, multiply it by two and add seven, and write out the result as Roman numerals. I won't say that I mastered COBOL, Lisp, and PL/1 in those thirteen weeks; but I learned how to read a manual and how to experiment with code.) After college, I was able to learn a few other programming languages in about a week of concentrated study as long as I had easy access to a compiler for that language, a good manual for that language, and no distractions. Note, however, that I have never claimed to be normal nor regular.