Automated Search and Replace

Hello, I have 2500 html pages with a url inside the code of each page. I need to replace that url with a link I have saved in a word document. For example [login to view URL] needs to have the dummy url found inside of the code and replaces with link #120 from my numbered word. I would like an automated script or someway way to keep the files updated as I add more pages. Any solutions are welcome. Must be able to run on OSX. Thank you.