[379] Improve mosquitto_passwd error messages.

Thanks to Jaimyn Mayer. Closes #379.

Bug: https://github.com/eclipse/mosquitto/issues/379

ChangeLog.txt

@@ -6,6 +6,7 @@ Broker:
 - For http only websockets clients, close files served over http in all cases
   when the client disconnects. Closes #354.
 - Fix error message when websockets http_dir directory does not exist.
+- Improve password utility error message. Closes #379.
 
 Client library:
 - Clients can now use TLS with IPv6.

src/mosquitto_passwd.c

@@ -377,35 +377,50 @@ int main(int argc, char *argv[])
 
 	OpenSSL_add_all_digests();
 
-	if(argc == 5){
+	if(argc == 1){
-		if(!strcmp(argv[1], "-b")){
+		print_usage();
-			batch_mode = true;
+		return 1;
-		}else{
+	}
-			fprintf(stderr, "Error: Unknown option '%s'\n", argv[1]);
+
+	if(!strcmp(argv[1], "-c")){
+		create_new = true;
+		if(argc != 4){
+			fprintf(stderr, "Error: -c argument given but password file or username missing.\n");
 			return 1;
+		}else{
+			password_file_tmp = argv[2];
+			username = argv[3];
 		}
-		password_file_tmp = argv[2];
+	}else if(!strcmp(argv[1], "-D")){
-		username = argv[3];
+		delete_user = true;
-		password_cmd = argv[4];
+		if(argc != 4){
-	}else if(argc == 4){
+			fprintf(stderr, "Error: -D argument given but password file or username missing.\n");
-		if(!strcmp(argv[1], "-c")){
+			return 1;
-			create_new = true;
-		}else if(!strcmp(argv[1], "-D")){
-			delete_user = true;
 		}else{
-			fprintf(stderr, "Error: Unknown option '%s'\n", argv[1]);
+			password_file_tmp = argv[2];
+			username = argv[3];
+		}
+	}else if(!strcmp(argv[1], "-b")){
+		batch_mode = true;
+		if(argc != 5){
+			fprintf(stderr, "Error: -b argument given but password file, username or password missing.\n");
 			return 1;
+		}else{
+			password_file_tmp = argv[2];
+			username = argv[3];
+			password_cmd = argv[4];
 		}
-		password_file_tmp = argv[2];
+	}else if(!strcmp(argv[1], "-U")){
-		username = argv[3];
+		if(argc != 3){
-	}else if(argc == 3){
+			fprintf(stderr, "Error: -U argument given but password file missing.\n");
-		if(!strcmp(argv[1], "-U")){
+			return 1;
+		}else{
 			do_update_file = true;
 			password_file_tmp = argv[2];
-		}else{
-			password_file_tmp = argv[1];
-			username = argv[2];
 		}
+	}else if(argc == 3){
+		password_file_tmp = argv[1];
+		username = argv[2];
 	}else{
 		print_usage();
 		return 1;