$ ls /tmp -al
-rw-------  1 user user 667030687 Apr 14 11:06 huge.log.gz

groupnum() {
  perl -pe 's;(?<=\d)(\d{3})(?=(\d{3})*(\D|$));.$1;g;'
}

$ ls /tmp -al | groupnum
-rw-------  1 user user 667.030.687 Apr 14 11:06 huge.log.gz