Got a much simpler solution working for dat.test.

docker-compose.yaml

@@ -1,3 +1,17 @@
+#
+# By default the dat.live folder will be mounted.
+# For testing you might like to switch to dat.test
+# The HLBDAT environment variable will do this for you.
+# If that variable is unset, dat.live will be used.
+# To use dat.test instead, run this...
+#
+# $ HLBDAT=dat.test docker compose up
+#
+# ...but if you're happy to play with the live data
+# this will do...
+#
+# $ docker compose up
+#
 services:
   app:
     image: php:8.2-apache
@@ -7,7 +21,7 @@ services:
     volumes:
       - ./app/:/var/www/html:Z
       - ./lib:/var/www/html/lib:Z
-      - ./dat.live:/var/www/html/dat:Z
+      - ./${HLBDAT:-dat.live}:/var/www/html/dat:Z
     networks:
       - labnet
   adm:
@@ -18,7 +32,7 @@ services:
     volumes:
       - ./adm/:/var/www/html:Z
       - ./lib:/var/www/html/lib:Z
-      - ./dat.live:/var/www/html/dat:Z
+      - ./${HLBDAT:-dat.live}:/var/www/html/dat:Z
     networks:
       - labnet
 networks: