Im sorry , i guess my question was ambiguous.
What im trying to do is replace all the hardcoded material with variables.
egs :
my $_out = `tcpreplay -i eth0 pkt_dump`;
i want to re-wrtie it as :
my $_cmd = "tcpreplay -i eth0 " ;
my $_out = `$_cmd pkt_dump`;
In effect , i want to replace all the hardcodes with variables in a lot many places.