How does the 'ls' command work in Linux/Unix?

To add to the answer, in The C Programming Language book (K&RC) they have given a small example on how to go about implementing ls. They have explained the datastructures and functions used very well.

To understand what ls does, you could take a gander at the OpenSolaris source: https://hg.java.net/hg/solaris~on-src/file/tip/usr/src/cmd/ls/ls.c.

If that´s overwhelming, on Solaris you start by using truss to look at the system calls that ls makes to understand what it does. Using truss, try:

truss -afl -o ls.out /bin/ls

then look at the output in ls.out

I believe that trace is the equivalent to truss in Linux.

ls doesn't fork. The shell forks and execs in order to run any command that isn't built in, and one of the commands it can run is ls.

ls uses opendir() and readdir() to step through all the files in the directory. If it needs more information about one of them it calls stat().