unix tip: find a character position in word

somebody asked on how to find a character position in a word/line on the unix.com forum

the question:
how to find a character position in a word/line?
eg.
Unix forum is the best site.

now in above line i want to find the character 'x' position
i.e 4

this is what i came up with:

$ echo "Unix forum is the best site." | grep -o "[-_a-zA-Z0-9\.]" | grep -n x
4:x

update:
one of the users has a very simple solution:

$ expr index "Unix forum is the best site." x
4