Thanks, Bill. I had considered that but decided not to use it due to the ambiguity I noted in my opening paragraph. Had penguin-attack wanted the single ASCII character SOH, instead of the string '<SOH>', that was covered by Ctrl-A (also noted).

[Side issue (struggling not to appear grossly pedantic): the charnames pragma has been distributed with Perl since at least v5.8.8 - the perldoc link (charnames) would provide the most recent documentation.]