commit-msg hook for git. Checks some format conventions.

commit-msg

#!/usr/bin/env python
# Put in .git/hooks/commit-msg and chmod +x it. 
from __future__ import print_function

import sys

def fail():
    print("Commit aborted.")
    sys.exit(1)

# Get the commit message
f = open(sys.argv[1]) 
msg = f.read()

lines = msg.split('\n')
first_line = lines[0]

if len(first_line)>50:
    print("Subject line is limited to 50 chars.")
    fail()
    
if first_line[0].islower():
    print("Subject line must be capitalized.")
    fail()
    
if first_line[-1]=='.':
    print("Subject line must not end in period.")
    fail()
    
if len(lines)>2: # If there is a body
    if lines[1]!="":
        print("Subject line and body must be separated with a blank line.")
        fail()
    for l in lines[2:]:
        if len(l)>72:
            print("Body must be wrapped at 72 characters max.")
            fail()
            
# Other convenient conventions not checked by the script:
# Use the imperative mood in the subject line
# Use the body to explain what and why vs. how


sys.exit(0)