s/\b(find)\b/ uc('repl') | ( $1 ^ uc($1) ) /eig;

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Only guaranteed to work for search strings and replacement strings consisting entirely of ASCII letters. Non-letter and accented characters won't work. EBCDIC won't work. It also only works if $1 and $find are the same length.

Update: Added clarification (by adding "guaranteed") and an extra failure mode.

In reply to Re: Respect case in substitution by ikegami
in thread Respect case in substitution by b4swine

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