Listing 1

 1: def factorial(n)
 2:  if n > 1
 3:   # casos mayor que 1, se usa la formula recursiva
 4:   # n! = n*(n-1)!
 5:   n * factorial(n-1)
 6:  else
 7:   # casos 0 y 1, devuelve 1
 8:   1
 9:  end
10: end

Output

ls -l *.zip