Drupal Security Updates Only for Multiple Sites

#!/bin/bash
# Script to do security updates only in Drupal 6 and Drupal 7 using drush version 6.2.0
# Note: drush up --security-only updates modules as well as core

# run `which drush` to find this path
drush='/usr/bin/drush'
# where your drupal sites live
site_dir='/var/www'
echo "Scanning sites directory for drupal installations"
cd $site_dir
for i in $(ls)
do
        a=$(readlink -f $i)
        # if your site files are in directories immediately
        # beneath your site_dir, i.e. /var/www/site.com,
        # then you don't need to `cd public_html'
        # just use `cd $a` below
        cd $a && cd public_html
        echo $(pwd)
        status=$($drush status | wc -l)
        # Count the lines on drush status to see if it's
        # actually a drupal site
        if [[ $status -gt 7 ]]
        then
                echo "Drupal site found"
                # `drush up` is interactive, so if you
                # don't want updates hit `n` for each site
                $drush up --security-only
        else
                echo "No Drupal site found in this directory"
        fi
        cd $site_dir
done
echo "Done with Drupal Security Updates"