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

my @letter = qw/ a b c x y z /;

my %subs;
my %counts;
foreach ( @letter ) {
  $subs{$_} = eval "sub { \$_[0] =~ tr/$_// }";
}

while ( <DATA> ) {
  foreach my $letter ( @letter ) {
    $counts{$letter} += $subs{$letter}->($_);
  }
}

print "$_: $counts{$_}\n" foreach @letter;

__DATA__
aedj dfas jijiojsdf dsfwfy jiox jiohjdfax jojojdjj, oiiia oioje asfdc oujsdfayx soujfosdxjpoiojfdxjljojaois jojojx jopjpx jojoijx joijiodfx

asdfasdf jjalsdf jlajkldf jojiojsd jiojasj ioj wwdn jojae jojocjoc joijss jiojwx jiojoxuiojy joiyu oiuouyy