CMGR Variable

[m7mdcc]

Hi , I'm trying to log CMGR variable for future troubleshoot like that :
exten => sms,n,System(echo '${STRFTIME(${EPOCH},,%Y-%m-%d %H:%M:%S)} - ${DONGLENAME} - ${CALLERID(num)}: ${BASE64_DECODE(${SMS_BASE64})} - PDU CODE : ${CMGR} - SMS : ${SMS}' >> /var/log/asterisk/sms.txt)

I can see SMS_BASE64 is same as SMS variable values , is that correct ?

CMGR Value is blank , there is no value .. normal ?

Thanks