This will give you all the characters including newline, spaces, etc.

use strict;
use Data::Dumper;
my %character_hash = ();

while (<DATA>) {
    map { $character_hash{$_}++ } split//,$_;
}

print Dumper(\%character_hash);

__DATA__
AFJIDIKSOIJFKDFS AKDFJIJDFJSF
QUEWITYYUERYUIYE ERUOIERTOUTUT
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