Shell Programming and Scripting

lyang0@lyang0-OptiPlex-755:~$ tr 'A-Z' 'a-z' <<< `printf 'DE:EF:BE:%02X:%02X:%02X\n' $((RANDOM%256)) $((RANDOM%256)) $((RANDOM%256))`
de:ef:be:20:a2:e8
lyang0@lyang0-OptiPlex-755:~$ GUEST_MAC=`tr 'A-Z' 'a-z' <<< `printf 'DE:EF:BE:%02X:%02X:%02X\n' $((RANDOM%256)) $((RANDOM%256)) $((RANDOM%256))``
bash: command substitution: line 1: syntax error near unexpected token `newline'
bash: command substitution: line 1: `tr 'A-Z' 'a-z' <<< '
DE:EF:BE:%02X:%02X:%02X\n: command not found

GUEST_MAC=$( printf "DE:EF:BE:%02X:%02X:%02X\n" $((RANDOM%256)) $((RANDOM%256)) $((RANDOM%256)) | tr 'A-Z' 'a-z' )