Counting regex pattern matches in one line using sed or grep?

Question

I want to count the number of matches there is on one single line (or all lines as there always will be only one line).

I want to count not just one match per line as in

Answer 1

This might work for you:

sed -n -e ':a' -e 's/123//p' -e 'ta' file | sed -n '$='

GNU sed could be written:

sed -n ':;s/123//p;t' file | sed -n '$='