The equivalent of
...
is
...

No, it is not. ls(1) will call getdents(2) until that doesn't return any more directory entries and finally output the list, while perl's readdir returns control after each call to getdents(2). Depending on the size of the directory to be read and the tasks to be done on each entry, it can make a big difference on distribution of iowait load (which, in sum, will be the same of course). I'm talking about linux here..