See perlre to see how could pattern be build and customize next code to read the file (using the name of file as argument to your program):

my %items;
while (<>)
{
   if (/my(searcheditem)pattern/)
   {
          $items{$1}++;
   }
}
foreach my $item (keys %items)
{
  do_what_do_you_want $items{$item};
}
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