sed replace new line character with space code example

Example 1: sed replace with 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 '\n'
#For example:
echo "123." | sed -E 's/([[:digit:]]*)\./\1|next line/' | tr '|' '\n'

Example 2: sed replace line with no line

Use d option at the end of sed command string for deleting line of matches.
sed -i "" "s/matching_pattern/d" file.txt