Попробуйте также
awk 'gsub("=[^&]*", "=FUZZ")' file
http://example.com/mall/mall/detail3.jsp?proID=FUZZ
http://example.com/mall/member/member/bookshelves/add.jsp?proID=FUZZ&productName=FUZZ
http://example.com/mall/bestbookTW//mall/detail3.jsp?proID=FUZZ&c=FUZZ&id=FUZZ