How can I use the UNIX shell to count the number of times a letter appears in a text file?

Question

I have a few text files and I\'d like to count how many times a letter appears in each?

Specifically, I\'d like to use the UNIX shell to do this, in the form of: cat fil

Answer 1

In this case, i'am counting the character "|":

expr `wc -c < filename` \- `tr -d \| < filename | wc -c`