REGEX-Escape for: https://www.pixiv.net/member_illaust.php?mode=medium&illust_id=

Your Input:
Result, the escaped string:
https\:\/\/www\.pixiv\.net\/member_illaust\.php\?mode\=medium&illust_id\=

What must the escaping look like for:
https://www.pixiv.net/member_illaust.php?mode=medium&illust_id=

The excaped text for use in a regex is:
https\:\/\/www\.pixiv\.net\/member_illaust\.php\?mode\=medium&illust_id\=