There must be a long-established idiomatic and elegant perl way to do this -- that I haven't found. I need a statement like:

s/\b$old\b/$new/g;
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where $new properly reflects the case of the first letter of $old.

Given $old="my"; $new="no"; this would transmogrify

My perl is my life.

into

No perl is no life.

(I can't include patterns in $new.)

thanks much -
Andy