SHELL

sed add newline

For substituting with newline use sed command to replace a match with a
not used char and tr command to replace that char with a newline '
'
#For example:
echo "123." | sed -E 's/([[:digit:]]*)./1|next line/' | tr '|' '
'

sed add lines

#add some lines from a file to 78 line of my file
sed -i -e '78r../../insert_file' File_you_change.txt 
#-i update the file , 

sed add new lines using a pattern

sed -i -e 's/yourpattern/yourpatternXXXTTTXXX/g' -i -e 's/XXXTTTXXX/
/g' file
									^add some unique pattern here
                                 # -i update the file , try without -i