/usr/bin/git-commits-since is in git-extras 1.9.1-2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | #!/bin/sh
SINCE="last week"
test $# -ne 0 && SINCE=$@
echo "... commits since $SINCE" >&2
git log --pretty='%an - %s' --after="@{$SINCE}"
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