I have the following text in a file:

XXXX

NNNN

YYYY

NNNN

ZZZZ

NNNN

I want to replace the NNNN to make it look like this:

XXXX

NNNN

DUTY FORECASTER:

YYYY

NNNN

DUTY FORECASTER:

ZZZZ

NNNN

DUTY FORECASTER:

How do I use sed to replace a variable with more than one line? Is there a better way of doing this without using sed?

I have tried the following to no avail:

sed 's/NNNN/"$value1"/g' testfile

sed 's/NNNN/'"$value1"'/g' testfile

sed 's/NNNN/${value1}/g' testfile

sed 's/NNNN/'"${value1}"'/g' testfile

I have also tried all of the above using double quotes. Any help is greatly appreciated. Thanks so much!