This script can be used when your drupal project has a list of hacked contrib modules and you haven't yet created the patches.

createpatch.sh

#!/bin/bash

echo "Please provide the directory having the original modules"
read modulesdir
cd $modulesdir
echo "Please provide the module directory that has the hacked modules eg. /User/username/sites/test/all/modules"
read repo_module_dir
echo "Please provide the path where the patches should be placed"
read patchpath

pwdir=$(pwd);
for files in $(ls); do
 echo $files;
 cd $pwdir/$files;
 git init
 git add .
 git commit -m "initial commit"
 rm -rf *
 echo $repo_module_dir/$files
 $(cp -rf $repo_module_dir/$files/ ./)
 git diff > $files.patch
 ls | grep "$files.patch"
 mv $files.patch $patchpath/
 $(cd ..)
done