This is information supplied at the whim of the browser. There is no guarantee that the referer is even valid since the browser can set it to anything it wants to.

Practically, this means you should have a reasonable default case in your script to handle the condition where referer isn't set or isn't one of the locations you want to act on.

Keep in mind of course that the referer could be set to one of your checked locations even though the browser has never even been there.

Also consider that the referer might be 'http://www.isu.edu/' instead of 'http://www.isu.edu' which both are probably the same place.

my $referer=$ENV{HTTP_REFERER};
if($referer eq 'place1')
{ ... }
elsif($referer eq 'place2')
{ ... }
else  #not set or not cared about
{
 #do default actions here
}
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