Update Drupal by patch file

drupal_create_patch.sh

# download a copy of current version and new updated drupal software.
drush dl drupal-<<original verion>>
drush dl drupal-<<new version>>

# Use diff to create a patch of directories.
diff -urN drupal-<<original verion>> drupal-<<new version>> > drupal-<<orig>>-to-<<new>>.patch

drupal_patch.sh

# Use patch to apply the patch from the Drupal site root directory. Patch reads from standard imput.

# Using –dry-run here does not apply the changes, just tells us what it would change. Do this first for testing.
cd /path/to/drupal/root
patch -p1 --dry-run < /path/to/drupal-<<orig>>-to-<<new>>.patch

# The -p1 option removes the top level part of the file path from each file that's listed in the patch.
# This is necessary because the files were originally in seperate directories.

# If all looks good here, run it.
patch -p1 < /path/to/drupal-6.20-to-6.22.patch

drupal_update_db.sh

# Run Update on the Database
cd /path/to/drupal/root
drush updatedb