new: ``compose config`` on validation success outputs the final docker-compose file on standard output instead of standard error.

bin/compose

@@ -2960,7 +2960,12 @@ case "$action" in
     config)
         ## removing the services
         services=($(get_master_services "${action_posargs[@]}")) || exit 1
-        launch_docker_compose "${compose_opts[@]}" "$action" "${action_opts[@]}" "${remainder_args[@]}"
+        ## forcing docker-compose config to output the config file to stdout and not stderr
+        out=$(launch_docker_compose "${compose_opts[@]}" "$action" "${action_opts[@]}" "${remainder_args[@]}" 2>&1) || {
+            echo "$out"
+            exit 1
+        }
+        echo "$out"
         warn "Runtime configuration modification (from relations) are not included here."
         ;;
     down)

test/base

@@ -1243,7 +1243,22 @@ EOF2
 cd "$test_tmpdir"
 
 export DISABLE_SYSTEM_CONFIG_FILE=true
-"$tprog" config
+out=\$("$tprog" config) || exit 1
+expected="networks:
+  static:
+    driver: bridge
+    ipam:
+      config:
+      - subnet: 172.25.1.0/24
+      driver: default
+services: {}
+version: '2.0'"
+
+[ "\$out" == "\$expected" ] || {
+    echo -e "DIFF:\n\$(diff <(echo "\$out") <(echo "\$expected"))"
+    exit 1
+}
+
 
 ## -- simple service provided