As you've been told, regexp -all -inline produces a list of things it has matched, where that list has several entries per match (first is the full match, subsequent entries are per capturing subexpression); its actual result here is |1) 1 |3) 3 |6) 6. What's going on with the foreach with the whole?
Well, the word whole is not special at all. It's just a variable name. The general form of that type of foreach is:
foreach listOfVariableNames listToIterateOver body
The {whole num} is a list of two variable names, so each iteration through $matches we pull off two elements of the list and assign them to each of the variables. If the body had instead been:
puts "whole = '$whole' num = '$num'"
The output would have been:
whole = '|1)' num = '1'
whole = '|3)' num = '3'
whole = '|6)' num = '6'
As you're actually not otherwise using whole, the effect is to ignore the whole-matches and just use the sub-expression matches. This is a fairly common pattern.