How do I insert a newline/linebreak after a line using sed

Question

It took me a while to figure out how to do this, so posting in case anyone else is looking for the same.

Answer 1

A simple substitution works well:

sed 's/pattern.*$/&\n/'

Example :

$ printf "Hi\nBye\n" | sed 's/H.*$/&\nJohn/'
Hi
John
Bye

To be standard compliant, replace \n by backslash newline :

$ printf "Hi\nBye\n" | sed 's/H.*$/&\
> John/'
Hi
John
Bye