php脚本重定向代码问题

Question

i'm using a php script for redirection after detecting the search word to my websiter from the search engines .

and my redirection code is working fine

but for some keywods i wat to stay in the same page. for that lines of code i'm getting a warning message in that pages.

Warning:  headers already sent 
          (output started at /home/friendsj/public_html/index.php:2) in
          /home/friendsj/public_html/index.php on line 20

below is the code i used in that pages

$ref=$_SERVER['HTTP_REFERER'];

if(strstr($ref,"test")){ 
  $url="http://www.howtomark.com/robgoyette.html";
}
else if(strstr($ref,"mu+word+gmail")){
    $url="http://www.howtomark.com/marketbetter.html";
}
else{
  if(strstr($ref,"how+to+market+better")){
  }    
}

if($url !=""){
  header("Location:$url");
}

Answer 1

Redirections are accomplished by setting an HTTP header, as the use of the header() function suggests. That means that you can only redirect before you start the document output. Whatever you start printing on line 2, do it later ;-)