Josselin wrote:
>>> I have an array   myArray = ["22", "31", "56", "89", "47"]
>>>
>>> I would like to produce a string like :    "22#31#56#89>47<"  where the
>>> last item must be :       >last_item<
Here you say that you want the second to last item to have no # after it,
>
> I should get "22#>31<",   the # must come after each item excepted the 
> last..

but here you say you want a # after it.
If you want no # sign, then Josselin's solution works.
If you want a # sign, just push that last item back on the array and 
join it with #

myArray = ["22", "31", "56", "89", "47"]
myArray2 = ["22", "47"]
myArray3 = ["47"]

arrays = [myArray, myArray2, myArray3]

arrays.each{|array| puts array.push('>' + array.pop.to_s + '<').join('#')}