Getting unterminated 's' command with sed (bash) - bash

Question

My final goal is to get a bunch of text above the COMMIT line in /etc/ufw/before.rules. I am trying to replace the COMMIT with something like this:
TEXT I WANT\nCOMMIT
I see this as an easy sed command: echo COMMIT | sed "s#COMMIT#${morerules}#g"
I have set the variable morerules to a string like this:
morerules="""
### Start HTTP ###
# Enter rule
-A ufw-before-input -p tcp --dport 80 -j ufw-http
-A ufw-before-input -p tcp --dport 443 -j ufw-http
# Limit connections per Class C
-A ufw-http -p tcp --syn -m connlimit --connlimit-above 50 --connlimit-mask 24 -j ufw-http-logdrop
# Limit connections per IP
-A ufw-http -m state --state NEW -m recent --name conn_per_ip --set
-A ufw-http -m state --state NEW -m recent --name conn_per_ip --update --seconds 10 --hitcount 20 -j ufw-http-logdrop
# Limit packets per IP
-A ufw-http -m recent --name pack_per_ip --set
-A ufw-http -m recent --name pack_per_ip --update --seconds 1 --hitcount 20 -j ufw-http-logdrop
# Finally accept
-A ufw-http -j ACCEPT
# Log
-A ufw-http-logdrop -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix \"[UFW HTTP DROP]\"
-A ufw-http-logdrop -j DROP
### End HTTP ##
"""
As you can see, I added a backslash to the quotations marks. Setting the variable is successful. When I run the command from above echo COMMIT | sed "s#COMMIT#${morerules}#g", this is the output:
sed: -e expression #1, char 9: unterminateds' command`
Is the error with my string or with my sed command? Also, I know other people have gotten this error, but none of their fixes seem to work.

Answer 1

To place a literal backslash before each newline in your replacement text, thus telling sed that it should be considered part of the same expression:
orig=$'\n'; replace=$'\\\n'
sed "s#COMMIT#${morerules//$orig/$replace}#g"
(Placing the values in variables makes it easier to implement this in a way that works across multiple versions of bash).