Variation on index method from Class String

Ok, so I wanted to find the indices of all occurrences of String 'A' within a larger String 'B'. The Ruby core String class's index and rindex methods do this for one value, but not for all of them.

A recursive solution made the most sense (note: ternary operator has to be on one line):

def indices(str, pos = 0)
!self.index(str, pos).nil? /
  ? (self.indices(str, self.index(str, pos)  + 1) /
  | [].push(self.index(str, pos))).sort : []
end

That gives an array of all of the indices in sorted order, and is actually quite cryptic. Here's a more readable version:

def indices(str, pos = 0)
 if (!self.index(str, pos).nil?)
    # Get the position of the current find
    x = self.index(str, pos)
    # Return the union of what you found
    #     and look for more occurrences
    [].push(x) | self.indices(str, x + 1)
 else
    # Basecase.  Return empty array for union "|"
    []
 end
end