Rewrite host with an iRule?

I would like to add a note that Joe's example is a good complete example that shows how to abstract the find and replace strings into variables. In reality, you could save some performance in the iRule by replacing the diff variable with the actual literal difference value. For example, "peanut.bean.com" is 15 characters and "apple.fruit.com" is also 15 characters, so instead of calculating: [string length $replace] - [string length $find], simply remove the line for setting the diff variable and also replace the $diff with 0. This optimization logic could also be applied to the find and replace variables as well. Simply using the strings "peanut.bean.com" and "apple.fruit.com" instead of the variables will improve the performance of the iRule. Basically, the more literals you can use vs. evaluating commands, the better the performance will be.