Extension Attribute Help

I am trying to use a script I found on another thread as an extension attribute to list all admin accounts on my laptops, excluding root and our main local admin account. I can run the script successfully on an idividual computer, but when I use it as an extension attribute, the attribute remains blank on the computer I successfully can run the script on. Anyone see what I'm missing?

#!/bin/sh

# Script to detect if a computer has a local admin account on it with a UID
# above 500

# Don't list these admin accounts
except=('localadmin1' 'root')

# Initialize array
list=()

# generate user list of users with UID greater than 500
for username in $(dscl . list /Users UniqueID | awk '$2 > 500 { print $1 }'); do
    # Checks to see which usernames are reported as being admins. The
    # check is running dsmemberutil's check membership and listing the
    # accounts that are being reported as admin users. Actual check is
    # for accounts that are NOT not an admin (i.e. not standard users.)
    if [[ $(dsmemberutil checkmembership -U "${username}" -G admin) != *not* ]] &&
           grep -qvFf <(printf '%s
' "${except[@]}") <(echo "${username}")
    then
        # Any reported accounts are added to the array list
        list+=("${username}")
    fi
done

# Prints the array's list contents
echo "<result>${list[@]}</result>"