#! 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

##</code><code>##

C:\test>530623
A => 0.5 0.25 0.25
T => 0.25 0.75 0.25
C => 0 0 0.25
G => 0.25 0 0.25