regex - How can I replace multiple empty lines with a single empty line in bash?

Question

I have a file that contains:

something



something else

something else again

I need a bash command, sed/grep w.e that will produce the following output

something

something else

something else again

In other words, I need to replace multiple blank lines with just a single blank line. grep/sed are line based. I've never found a BASH solution that would work on multi-line regex patterns.

Answer 1

For BSD-derived systems (including GNU):

You just need cat with the -s option which causes it to remove repeated empty lines from its output:

cat -s

From man page: -s --squeeze-blank: suppress repeated empty output lines.