git-last

#!/usr/bin/env python

"""Prints the last checked out branches (i.e. HEAD, @{-1}, @{-2}, ...), one per line.

Duplicates will be skipped, so the line number does not necessarily correspond to the |n| in `@{-n}`.
"""

import re
import subprocess

lines = subprocess.check_output(['git', 'reflog']).splitlines()

branches = set()

for line in lines:
  match = re.match(r'^[0-9a-f]+ HEAD@\{\d+\}: '
                   r'checkout: moving from \S+ to (\S+)$', line)
  if match:
    branch = match.groups()[0]
    if branch == 'HEAD':
      continue

    if not branch in branches:
      branches.add(branch)
      print branch