pre-commit hook to re-write the TravisCI Badge with the current branch. Save as `.git/hooks/prepare-commit-msg` (without the .py extension)

prepare-commit-msg.py

#!/usr/bin/env python
"""
Referencing current branch in github readme.md[1]

This pre-commit hook[2] updates the README.md file's
Travis badge with the current branch. Gist at[4].

[1] http://stackoverflow.com/questions/18673694/referencing-current-branch-in-github-readme-md
[2] http://www.git-scm.com/book/en/v2/Customizing-Git-Git-Hooks
[3] https://docs.travis-ci.com/user/status-images/
[4] https://gist.github.com/DrSAR/eb50d9b2b993384267db4ee9fd5e210f
"""
import subprocess
import re

# Hard-Coded for your repo (ToDo: get from remote?)
REPOurl=subprocess.check_output(['git','config','--local', 'remote.origin.url']).decode()
GITHUB_USER=re.match('.*:([a-zA-Z0-9]*)\/', REPOurl).groups()[0]
REPO=re.match('.*\/([a-zA-Z0-9]*).git', REPOurl).groups()[0]

print("Starting pre-commit hook for {0} on {1}...".format(GITHUB_USER, REPO))

BRANCH=subprocess.check_output(["git",
                                "rev-parse",
                                "--abbrev-ref",
                                "HEAD"]).strip()

# String with hard-coded values
# See Embedding Status Images[3] for alternate formats (private repos, svg, etc)

#  [![Build Status](https://travis-ci.org/
#  joegattnet/joegattnet_v3.png?
#  branch=staging)][travis]

# Output String with Variable substitution
travis="###branch: {BRANCH} [![Build Status](https://travis-ci.org/" \
       "{GITHUB_USER}/{REPO}.svg?" \
       "branch={BRANCH})](https://travis-ci.org/{GITHUB_USER}/{REPO})\n".format(BRANCH=BRANCH.decode(),
                                            GITHUB_USER=GITHUB_USER,
                                            REPO=REPO)

sentinal_str="[![Build Status]"

readmelines=open("README.md").readlines()
with open("README.md", "w") as fh:
    for aline in readmelines:
        if sentinal_str in aline and travis != aline:
            print("Replacing:\n\t{aline}\nwith:\n\t{travis}".format(
                   aline=aline,
                   travis=travis))
            fh.write(travis)
        else:
            fh.write(aline)

subprocess.check_output(["git", "add", "README.md" ])

print("pre-commit hook complete.")