-p   causes perl to assume the following  loop  around  your
          script,  which makes it iterate over filename arguments
          somewhat like sed:

               while (<>) {
                    ...       # your script goes here
               } continue {
                    print;
               }

          Note that the  lines  are  printed  automatically.   To
          suppress  printing use the -n switch.  A -p overrides a
          -n switch.