Count the appearence of certain chars (See related posts)

#!/usr/bin/perl
# Count the appearence of certain chars using regular expression query
#


$string="MNVDPFSPHSSDSFAQAASPARKPPRGGRRIWSGTREVIAYGMPASVWRDLYYWALKVSWPVFFASLAALFVVNNTLFALLYQLGDAPIANQSPPGFVGAFFFSVETLATVGYGDMHPQTVYAHAIATLEIFVGMSGIALSTGLVFARFARPRAKIMFARHAIVRPFNGRMTLMVRAANARQNVIAEARAKMRLMRREHSSEGYSLMKIHDLKLVRNEHPIFLLGWNMMHVIDESSPLFGETPESLAEGRAMLLVMIEGSDETTAQVMQARHAWEHDDIRWHHRYVDLMSDVDGMTHIDYTRFNDTEPVEPPGAAPDAQAFAAKPGEGDARPV";

$neg = ($string =~ tr/[DE]//);
$pos = ($string =~ tr/[RK]//);
$his = ($string =~ tr/[H]//);
$total = $pos+$his-$neg;
$totalNoHis = $pos-$neg;

print "NEG = $neg ; POS = $pos ; HIS = $his; TOT = $total (without HIS = $totalNoHis)\n";