use Data::Dumper;

my @inst = ( 'AAA', 'ATG', 'TTT', 'GTC' );
get_pwm(@inst);

sub get_pwm {

    my @data = @_;
    my %pwm;
    foreach my $line (@data) {

        ++$pwm{ substr $line, $_, 1 }[$_] for 0 .. length($line) - 1;
    }

    my $n = $.;
    @$_ = map { $_ ? $_ / $n : 0 } @$_ for values %pwm;  # Line 26

    print Dumper \%pwm;
    print "$_ => @{ $pwm{ $_ } }" for keys %pwm;

    return;
}