@letter = qw( a b c w x y );
for ($n=0; $n<6; $n++){
$x = $letter[$n];
$m = 0;

open (DATA, "data.txt") ||
die "Could not open source data file.";
while (<DATA>) {
$cnt = eval "tr/$x/$x/";
$m += $cnt;
}

print "$x  $m";
}