Hi ,

 
           use CGI qw(:all);
           print "Content-type : text/html\n\n";
           # print $header;
           # all your lines come here
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and run the cgi from commandline and check if the snmpwalk returns or is the permission granted for your group or users ,the permission to run the snmpwalk can be that which does not let you get in the foreach loop and print stuff , so look at these changes intiallay and you may have the $swalk printed to the STDOUT , I guess