Php shell_exec casperJS

I installed phantomJS and casperJS on my Linux machine and added symlinks to / usr / local / bin / casperjs and / usr / local / bin / phantomjs. if i login via ssh everything works fine.

but i want to call casperjs in php script with shell_exec:

shell_exec('/usr/local/bin/casperjs');

      

        
        
        
      

    

I also added to my php include_path:.: / Usr / local / bin / casperjs

but I only get "NULL" as output from exec command - how can this be done? Can anyone please help? how can I use casperjs on the web hosting directory which is / var / www /?