in reply to Regexing a block of text in between patterns
perl -lne "print $first++? q{</div><div>}:q{<div>} and next if 0==inde +x $_, "[Sidenote"; print; print q{</div>} if eof" letters.txt [download]
print+qq(\L@{[ref\&@]}@{['@'x7^'!#2/"!4']});