git diff HEAD\^ HEAD

git_diff_head.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

from subprocess import call
import sys

if __name__ == '__main__':

    if len(sys.argv) == 1:
        old_n = 1
        new_n = 0
    elif len(sys.argv) == 2:
        old_n = int(sys.argv[1])
        new_n = 0
    else:
        old_n = int(sys.argv[1])
        new_n = int(sys.argv[2])

    old_commit = "HEAD" + "^"*old_n
    new_commit = "HEAD" + "^"*new_n
    call(["git", "diff", old_commit, new_commit])