#!/usr/bin/perl
use warnings;
use strict;

# open file
my $file = shift @ARGV;
open FILE1, '<', $file or die "Can't open '$file': $!";

my %caseCount;
# Use a while loop to read through the data
while ( <FILE1> ) {
    my $caseNumber = ( split /\t/ )[ 1 ];
    $caseCount{ $caseNumber }++;
}

# close the file you don't need it any more
close FILE1;

#do something here with values in %caseCount