The use of this variable anywhere in a program imposes a considerable performance penalty on all regular expression matches.

s/(?<=[a-zA-Z])([12])/ $1 == 1 ? 2 : 1 /eg;
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heh. I had a capture and $1 in there orginally, and then to be 'clever' changed it to $& to save a couple characters :)

As far as the positive look-behind, y, it's not necessary -- just (since it's zero-width) saves having to reference a second capture in the replacement:

s/([a-z])([12])/ $1 . ($2 == 1 ? 2 : 1) /eig;
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(i think the /i is less efficient, too.. too many different ways to write this one)

Thanks !!!! The 3 lines of code below work! The first char will always be a capital letter and the 2nd char will always be a number. Then I just need to change the number. So, I think the "." in line 3 will also be ok? I am curious how lines 2 and 3 below work.

line 2 below ... it searches for a leter in lowercase. Then it joins what it changes in the next step.... If $2 is equal to 1 then change it to 2. If $2 is equal to 2, then it changes it to 1.

Is the letter $0 and the number $1 ? I assume so.

example input is "D1"


   # s/(?<=[a-zA-Z])([12])/ $1 == 1 ? 2 : 1 /eg;
   # s/([a-z])([12])/ $1 . ($2 == 1 ? 2 : 1) /eig;
   s/(.)([12])/ $1 . ($2 == 1 ? 2 : 1) /eig; 
   
this might work:
   s/([A-Z])([12])/ $1 . ($2 == 1 ? 2 : 1) /eig;
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THANKS TO EVERYONE !!!! Kevin