Copy, paste and rename an existing filter folder like censor or activitynames as a starting point. You'll need to know some php & reg expressions to get the specifics - sorry can't be much help there. Have attached the original hacked filter I got an IT tutor to do for me. We've since moved onto a more advanced solution but the principles should be similar to your requirements.
The filter has the following logic:
- Check for urls
- Check if the URL already has the the ezproxy prefix
- Loop thru the text checking for the defined domains and adding the ezproxy prefix where necessary
- Array of domains we are interested in
- Identify URLs with expired ezproxy domains (foundincorrect)
- Substitute a correct domain for the incorrect one (changeincorrect)