# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(.+\..+?\\/.+?\\/).+/$1/gm;t' <<< "http://www.example.com/part1/part2/part3/part4
http://www.example.org/part1/part2/part3/part4
http://subdomain.example.org/part1/part2/part3/part4
http://subdomain1.subdomain2.example.org/part1/part2/part3/part4"
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