fix: a variable reference error.

Author: Zerorigin

root/etc/s6-overlay/s6-rc.d/init-mariadb-initdb/run

@@ -6,7 +6,7 @@ start_mariadb() {
     mariadbd --datadir="${DATADIR}" --init-file="${tempSqlFile}" --user=abc &
     pid="$!"
     RET=1
-    while [[ RET -ne 0 ]]; do
+    while [[ ${RET} -ne 0 ]]; do
         mariadb -uroot -e "status" >/dev/null 2>&1
         RET=$?
         sleep 1