$ cat test.pl
use strict;
use warnings;

use Text::CSV_XS;

my $csv = Text::CSV_XS->new ({ binary => 1, sep_char => "|", auto_diag => 1 });

open my $fh, "<", "Proj20101111.csv" or die $!;

my @hdr = map { lc } @{$csv->getline ($fh)};
my %rec;
$csv->bind_columns (\@rec{@hdr});
my %count;
while ($csv->getline ($fh)) {
    $count{$rec{client_id}}++;
    }
printf "%-8s %7d\n", $_, $count{$_} for sort keys %count;
$ perl test.pl
104167      1001
116571      4004
BLANK      24024