this is a python script intended for use with unity projects using SVN for version control

pre-commit.py

#! /usr/bin/python

# This script is intended for use with unity projects using subversion for version control systems
#
# This pre-commit hook will prevent a commit that includes files in the Assets/ folder
# that do not have a companion .meta file.
# Adding asset files without meta files creates a scenario where multiple people
# will have conflicting meta files, causing conflicting settings for imported assets, 
# conflicts over who owns the authoritative .meta file, endless confusing notifications about .meta files
# needing to be updated or committed, and generally leads to the dark side. 


import os
import sys
import subprocess

import random


LOOK='svnlook'
WARN='Found files with no matching meta files in commit'

def main(argv):
	result = 'success'
	txn = argv[1]
	repo = argv[2]
	commit_info = get_commit_info(txn, repo)
	
	if 'META_OVERRIDE' in commit_info['comment']:
		exit('override found... skipping', 0)
		return

	raw_file_dump = svn_look('diff', txn, '-t', argv[2])
	committed_files = files_changed(raw_file_dump)
	lonely_files = []

	for f in committed_files:
		# Skip any files not contained in the Assets directory; these are not under our control.

		if not '/Assets/' in f:
			continue	
		if not '.meta' in f:
			meta = f + '.meta'
			if not meta in committed_files:
				lonely_files.append(f)
	
	if(len(lonely_files) > 0):
		result = WARN + '\n' + 'The following files have no matching meta file.\n' + '\n'.join(lonely_files) + '\n' + 'Open up the unity project and meta files will be auto-generated'
	
	exit(result, len(lonely_files))

def files_changed(files):
  def filename(line):
      return line[4:]
  def added(line):
      return line and line[0] in ("A")
  return [
      filename(line)
      for line in files.split("\n")
      if added(line)]

def get_commit_info(repo, revision ):
	comment = svn_look('log', repo, '-t', revision)
	author = svn_look('author', repo, '-t', revision)
	files = svn_look('changed', repo, '-t', revision)

	commit_info = {'revision' : revision, 'comment' : comment, 'author': author, 'files':files}
	return commit_info

def svn_look( *args ):
	p = subprocess.Popen(' '.join([LOOK] + list(args)), stdout=subprocess.PIPE, shell=True, stderr=subprocess.STDOUT )
	out, err = p.communicate()
	return out

def exit(msg, status):
	import os.path
	stream = sys.stderr or sys.stdout
	stream.write(msg)
	sys.exit(status)

if __name__ == '__main__':
	main(sys.argv)

pre-commit.py

python 2.7

this is a python script is intended for use with Unity3D projects using SVN for version control

depending on your particular svn configuration, you will lilely have to rename pre-commit.py to 'pre-commit'

place this file in your path/to/repo/hooks/ directory, and SVN should take care of the rest

this script does not require any additional python modules

comment spelling errors fix and explicit '/Assets/' folder update courtesy of @danfranklinusa