Just as C only has very few statements implemented in the language itself, UNIX has only very few commands in the resident part of the operating system. They both are originally solely text-based. Both UNIX and C are case-sensitive. Most operating systems make no difference between the filenames c.txt , C.txt , c. For UNIX, each of those names points to a different file.
C works exactly the same.
This is, by the way, something quite odd for programming languages too. It is quite visible there is an obvious link between UNIX and C, and I think this is one of the reasons that both UNIX and C are still very popular after all those years. On to C programming tips and tricks .