The correct answer is use the HTML Agility Pack and parse the html properly
However, in regards to you comment
I have 13000 sharepoint sites and for each site I have to parse the
master page and remove the above specific script tag
You can use something nasty like this i guess :/
Regex.Replace(yourPage, @"<script src=""https://cdn.getsmartcontent.com/.+?\/script>", String.Empty);
You could use the multiline option i guess, but this is still a bad idea
Note/Disclaimer/Warning : See bold comment
5
solved Search for a url in a string and remove enclosing tag