Can I use the sed command to replace multiple empty line with one empty line?

Question

I know there is a similar question in SO How can I replace mutliple empty lines with a single empty line in bash?. But my question is can this be implemented by just using the <

Answer 1

Give this a try:

sed '/^$/N;/^\n$/D' inputfile

Answer 2

You can do this by removing empty lines first and appending line space with G command:

sed '/^$/d;G' text.txt

Edit2: the above command will add empty lines between each paragraph, if this is not desired, you could do:

sed -n '1{/^$/p};{/./,/^$/p}'

Or, if you don't mind that all leading empty lines will be stripped, it may be written as:

sed -n '/./,/^$/p'

since the first expression just evaluates the first line, and prints it if it is blank.

Here: -n option suppresses pattern space auto-printing, /./,/^$/ defines the range between at least one character and none character (i.e. empty space between newlines) and p tells to print this range.