# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/^(?!(?:§|[A-Z]+$)).{0,3}(?:[\r\n]+|\z)//gm;t' <<< "§day
DOG
Happy
Monday
Now
Yes
Sunday
§new day.txt
DIY
Leg
Books
Car
Home
abc"
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html