To count commits in a date range in the current branch, follow these steps:
git rev-list --count HEAD --since="Dec 3 2015" --before="Jan 3 2016"
If you want the counting for all branches to be used at a time - additionally optional
git rev-list --count --since="Dec 3 2015" --before="Jan 3 2016" --all
if you want to exclude merge commands, use the --no-merges option
git rev-list --count --since="Dec 3 2015" --before="Jan 3 2016" --all --no-merges
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