Find current position of keyword

I have some code which collects keywords used by people visiting my website, and stores them in to a database. What i would like is for somebody to write a peice of code that will take these keywords and find where my website ranks for them in the following search engines, Google Bing, Yahoo and then to store the results in the mysql database next to the keywords. Ideally i would like this code write so that i can incorporate it in to my existing code, so for example we would catch the keyword as the variable $string, your code would then take that variable look up the websites position which would be another variable $website and then return the results in to a mysql database adding the date and time to the two variables.