Clarified a comment

Allowed values are A-F, a-f and 0-9. Not a-z or A-Z

hostid.sh

@@ -7,7 +7,7 @@
 
 if [[ -n "$1" ]]; then
   host_id=$1
-  # chars must be 0-9, a-z, A-Z and exactly 8 chars
+  # chars must be 0-9, a-f, A-F and exactly 8 chars
   egrep -o '^[a-fA-F0-9]{8}$' <<< $host_id || exit 1
 else
   host_id=$(hostid)