How do I replace multiple newlines with a single one with Perl's Regular Expressions?

Question

I've got a document containing empty lines (\n\n). They can be removed with sed:

echo $'a\n\nb'|sed -e '/^$/d'

But how do I do that with an ordinary regular expression in perl? Anything like the following just shows no result at all.

echo $'a\n\nb'|perl -p -e 's/\n\n/\n/s'

Answer 1

You need to use s/^\n\z//. Input is read by line so you will never get more than one newline. Instead, eliminate lines that do not contain any other characters. You should invoke perl using

perl -ne 's/^\n\z//; print'

No need for the /s switch.