Thanks! Despite the murkiness of my question, you provided the magic I was looking for:

 my $match_str="[tr]x_n1(?!\\d)";

It was the zero-width negative look-ahead assertion  (?!\d) that I was looking for

BTW your use of map is spinning my head :) I will also be looking into qr

In reply to Re^2: regular expression to match specific members of a bus_name by boleary
in thread regular expression to match specific members of a bus_name by boleary

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