tube categories auto redirection
 

Hey,
I see lots of muliniche type tube redirecting traffic on their website according to the category that the surfer came from on the previous website. for example if http://site.com/granny.html sent them a visitor, the next site will pull the word 'granny' from the http referer url and then redirect the surfer to its granny niche url . I guess this is done by php code that fetches the http refferer and pull the relevant words from it.
Anyone knows how do do this with php code ?

so... anyone ?