I am trying to write a regex that adds extension to my domain name. For example google, I need a regex expression that will return www.google .com
You can append like this:
... | rex field=YourFieldHere mode=sed "s/$/YourExtensionStringHere/"
Or like this:
... | eval YourFieldHere = YourFieldHere . "YourExtensionStringHere"
What does your raw data look like? In other words, please show us the text you want a regex string to match.