Bash script to find the frequency of every letter in a file

Question

I am trying to find out the frequency of appearance of every letter in the english alphabet in an input file. How can I do this in a bash script?

Answer 1

Here is a suggestion:

while read -n 1 c
do
    echo "$c"
done < "$INPUT_FILE" | grep '[[:alpha:]]' | sort | uniq -c | sort -nr