# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/\\/(?!.*\.(?:php|jpg|html)$)[^\\/]+$/$0\\//gm;t' <<< "www.mysite.com/page
www.mysite.com/page/
www.mysite.com/file.php
www.mysite.com/file.jpg
www.mysite.com/file.html
www.mysite.com/file.doc"
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