Grabs the currently logged in user and checks to see if they have an associated AppleID.

Get Current Users AppleID.sh

#!/bin/bash

# (C) Andrew Worth Carson
# MIT License: https://andrewworthcarson.com/mit_license.html

username=$(/usr/bin/python -c 'from SystemConfiguration import SCDynamicStoreCopyConsoleUser; import sys; username = (SCDynamicStoreCopyConsoleUser(None, None, None) or [None])[0]; username = [username,""][username in [u"loginwindow", None, u""]]; sys.stdout.write(username + "\n");')
if [[ "${username}" == "" ]]; then
    echo "No user currently logged in."
    exit 1
else
    appleid=$(! dscl . readpl "/Users/${username}" dsAttrTypeNative:LinkedIdentity appleid.apple.com:linked\ identities:0:full\ name | awk -F'full name: ' '{print $2}')
    if [[ "${appleid}" == "" ]]; then
        echo "AppleID was not found."
        exit 2
    else
        echo "${appleid}"
        exit 0
    fi
fi

Licensing, yo.