in reply to <> to read command line options?

slackcub wrote:..They use that to read they list of arguments **from the command line...

That is not SO! Sir!! :). I suppose you presumed that.
Reading from the explanation of solution given by the author(s) of the book on that exercise:

That second line of code is too confusing *(that is referring to push @numbers, split while <>;
), isnít it? Well, we did that on purpose. Although we recommend that you write clear code, some people like writing code thatís as hard to understand as possible, so we want you to be prepared for the worst. Someday, youíll need to maintain confusing code like this.
Since that line uses the while modifier, itís the same as if it were written in a loop like this:
while (<>) { push @numbers, split; }
Thatís better, but maybe itís still a little unclear. (Nevertheless, we donít have a quibble about writing it this way. This one is on the correct side of the ďtoo hard to understand at a glanceĒ line.) The while loop **is reading the input one line at a time (from the userís choice of input sources, as shown by the diamond operator), and split is, by default, splitting that on whitespace to make a list of wordsóor in this case, a list of numbers. The input is just a stream of numbers separated by whitespace, after all. Either way you write it, then, that while loop will put all of the numbers from the input into @numbers.

* included by me for clarity.
** Bold text were used for emphasis.

If you tell me, I'll forget.
If you show me, I'll remember.
if you involve me, I'll understand.
--- Author unknown to me