#! perl -slw
use strict;

my %pwm;
while( my $line = <DATA> ) {
    chomp $line;
    ++$pwm{ substr $line, $_, 1 }[ $_ ] for 0 .. length( $line ) -1;
}
my $n = $.;
@$_ = map{ $_ ? $_ / $n : 0 } @$_ for values %pwm;

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

__DATA__
AAA
ATG
TTT
GTC