I find your request odd. What is it that you want to optimise here? Sure you probably shave a few nanoseconds off the run time of this code by replacing it whith a s/// but really this code doesnt do enough for it to be an optimisation candidtate.

s/([^\\\/]+)$/$temp1.$temp2.$1/;
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The only reason I can think of to change your code is to make it easier to read.