Perl match newline in `-0` mode
I've got a loverly bunch of coconut trees.

Newlines!

Bahahaha
Newlines!
the end.

I've got a loverly bunch of coconut trees.

NEWLINES!

Bahahaha
Newlines!
the end.

perl -p -e 's@Newlines!@NEWLINES!@g' input.txt

perl -p -e 's@nNewlines!n@nNEWLINES!n@g' input.txt

perl -p -e 's@(?<=n)Newlines!(?=n)@NEWLINES!@g' input.txt

perl -0p -e 's@(?<=n)Newlines!(?=n)@NEWLINES!@g' input.txt

perl -0p -e 's@(?<=)Newlines!(?=)@NEWLINES!@g' input.txt

perl -0pe 's@(?<=nn)Newlines!(?=nn)@NEWLINES!@g'

perl -0p -i.bk -e 's/nnNewlines!nn/nnNEWLINES!nn/g' input.txt

perl -0777 -pe 's/nnNewlines!(?=nn)/nnNEWLINES!/g'

perl -ne 'push @buffer, $_; $buffer[1] = "NEWLINES!n" if @buffer == 3 && '
      -e 'join("", @buffer) eq "nNewlines!nn"; '
      -e 'print shift @buffer if @buffer == 3; END { print @buffer }'