Thank you for a reply. I'm sorry to say I think I am still a bit too inexperienced in the Perl language to follow the code in your reply fully but I have had a go and tried to answer your questions as fully as I can;

What is my RegExp trying to match? I am trying to match and substitute the words in the string $_ by asking the user to input the correct string of number values. Originally I tried to match and substitute in each 'if' decision after the user input, however doing it this way I could not see a way to match to any string other than the first available without using a string literal.

i.e. $_ = "three, four" I could not see a way to match to 'four' without using the literal, whereas, as I understood it the power of a RegExp came from it being able to find something in a string without a literal constant.

In essence I suppose what I am trying to do is: Psuedo-

1st substitute/([A-Z][a-z][\W][\b])/<userinput>/;
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then
2nd substitute/(NOT THIS ONE[A-Z][a-z][\W][\b])(THIS ONE[A-Z][a-z][\W]
+[\b])/<userinput>/;
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then
3rd substitute/(NOT THIS ONE[A-Z][a-z][\W][\b])(AND NOT THIS ONE[A-Z][
+a-z][\W][\b])(BUT THIS ONE[A-Z][a-z][\W][\b])/<userinput>/;
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Does that make any kind of sense?

Your first RegEx(A-Za-z.\b) matches nothing because no words in the string are 2-characters in size, adding a plus to the lower case set a-z+ would match the first word, but as I understand it . is capable of matching nothing as well as anything, therefore I beleive it would match nothing and the next character in the match would be a comma when the match is actually looking for a break.

Why does the second regex match something, but only once when you want it to match several times? I'm unsure about this part so I can't answer this question easily, (?: , | \b)). ? allows the preceeding character to be optional (but there is no preceeding character?) and I can't see the use of a colon in this context. I understand however that the comma is a literal constant to look for, OR a break. '/x' I have not yet come across. Has it only matched once because it is not part of a loop to tell it to match as many times as I want? I don't want the comma, so perhaps look only for A-Za-z but then how then do I ignore these the second time I want to match? If I must match only once (as I originally had tried to do, then why does Perl not find anything for $2 $3 and $4?

As for Update 1 & 2 I'm afraid they're far beyond my capablities at this moment in time, I realise they're more than likely a cleaner way to write the code, I was simply trying to write a program for myself to show I understood RegExp (but clearly that is not the case!), I'm afraid the code in the two updates are far too advanced for me at this moment ;/