-s   enables some rudimentary switch parsing for switches on
          the  command  line after the script name but before any
          filename arguments (or before a --).  Any switch  found
          there  is removed from @ARGV and sets the corresponding
          variable in the  perl  script.   The  following  script
          prints "true" if and only if the script is invoked with
          a -xyz switch.

               #!/usr/bin/perl -s
               if ($xyz) { print "true\n"; }