GitHub-like commit differences

git-cdiff

#!/usr/bin/env python

"""
Checks the commit difference between current branch and target branch
a la GitHub.

Usage:
    $ git cdiff upstream/master
    This branch is 5 commits ahead, 10 commits behind upstream/master.

Installation:
    - Make executable: chmod 755 git-cdiff
    - Make accessible in path
"""

import subprocess
import sys


class GitException(Exception):
    pass


def commit_diff(target):
    cmd = ['git', '--no-pager', 'log', '--oneline', target]

    process = subprocess.Popen(cmd,
                               stdout=subprocess.PIPE,
                               stderr=subprocess.PIPE)

    std_out, std_err = process.communicate()

    if std_err:
        raise GitException(std_err.strip())
    else:
        return len(std_out.strip().splitlines())

if __name__ == '__main__':
    try:
        branch = sys.argv[1]
        print("This branch is {} commits ahead, {} commits behind {}".format(
            commit_diff('{}..'.format(branch)),
            commit_diff('..{}'.format(branch)),
            branch))
    except IndexError:
        print('Target branch name required')
        exit(1)
    except GitException as e:
        print(e.message)
        exit(1)