fix: -container-filter should override the env var

Author: buchdag

README.md

@@ -157,7 +157,7 @@ Environment Variables:
   DOCKER_CERT_PATH - directory path containing key.pem, cert.pem and ca.pem
   DOCKER_TLS_VERIFY - enable client TLS verification
   DOCKER_CONTAINER_FILTERS - comma separated list of container filters for inclusion by docker-gen.
-    Filters supplied through this variable override filters supplied through the -container-filter options.
+    Filters supplied through this variable are ignored if -container-filter is provided.
 ```
 
 If no `<dest>` file is specified, the output is sent to stdout. Mainly useful for debugging.

cmd/docker-gen/main.go

@@ -87,7 +87,7 @@ Environment Variables:
   DOCKER_CERT_PATH - directory path containing key.pem, cert.pem and ca.pem
   DOCKER_TLS_VERIFY - enable client TLS verification
   DOCKER_CONTAINER_FILTERS - comma separated list of container filters for inclusion by docker-gen.
-    Filters supplied through this variable override filters supplied through the -container-filter options.
+    Filters supplied through this variable are ignored if -container-filter is provided.
 `)
 	println(`For more information, see https://github.com/nginx-proxy/docker-gen`)
 }
@@ -152,8 +152,8 @@ func initFlags() {
 	flag.Usage = usage
 	flag.Parse()
 
-	// override containerFilter with DOCKER_CONTAINER_FILTERS environment variable
-	if filtersEnvVar, found := os.LookupEnv("DOCKER_CONTAINER_FILTERS"); found && filtersEnvVar != "" {
+	// set containerFilter with DOCKER_CONTAINER_FILTERS if it's set and no -container-filter option was provided
+	if filtersEnvVar, found := os.LookupEnv("DOCKER_CONTAINER_FILTERS"); found && len(containerFilter) == 0 {
 		var nonBlankFilters []string
 
 		for filter := range strings.SplitSeq(filtersEnvVar, ",") {