Git alias:
log-of-count-and-format = "!f() { format=\"$1\"; shift; git log $@ --format=oneline --format="$format" | awk '{a[$0]++}END{for(i in a){print a[i], int((a[i]/NR)*100) \"%\", i}}' | sort -nr; }; f"
Example:
git log-of-count-and-format <format>
Compare git log-of-format-and-count.