($firstLetter)= ($file_name=~ /^(.)/);
push(@{$hash{uc($firstletter)}}, $infoline);

##</code><code>##

$hash{'A'} -> [ infolineA1, infolineA2 ... ]
$hash{'B'} -> [ infolineB1, infolineB2 ... ]

##</code><code>##

foreach $letter (sort keys %hash) {
    print $letter;
    foreach $infoline (@{$hash{$letter}}) {
        print $infoline;
    }
}