#!/usr/bin/perl -w
# get_char_probability.pl - Don Yang (uguu.org)
#
# 2015-06-05

use strict;

# Initialize zero frequency for each character
my @freq = ();
$freq[$_] = 0 foreach 0..25;

# Get character frequencies
while( my $line = <> )
{
   foreach my $c (unpack 'C*', $line)
   {
      if( chr($c) =~ /[a-z]/ )
      {
         $freq[$c - ord('a')]++;
      }
      elsif( chr($c) =~ /[A-Z]/ )
      {
         $freq[$c - ord('A')]++;
      }
   }
}

# Get total character count
my $size = 0;
$size += $_ foreach @freq;
unless( $size > 0 )
{
   die "No alpha characters found in input\n";
}

# Output probabilities
print '@f = (', "\n";
for(my $i = 0; $i < 26; $i++)
{
   print $freq[$i] / $size, ",  # ", chr($i + ord('a')), "\n";
}
print ");\n";