"Lewei Xu" <23*0*0*8@s*u*e*t*u*a*e*u*a*> wrote: We can trivially call a command-line utility from within a C program by using for() and execl(). But the mkdir program does little more than call the mkdir() system-call, which we can do from within our own program. If the action performed by an external program was far more significant, such as sort or zip, then it'd make far more sense to spawn the external program.