Cleanup command error handling in "service"

- Add helper for checking number of arguments
 - Add helper for printing "please read help" message

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>

servicecmd/disable.c

@@ -31,18 +31,15 @@ static int cmd_disable(int argc, char **argv)
 	char *linkname, *ptr;
 	struct stat sb;
 
-	if (argc < 2 || argc > 3) {
+	if (check_arguments(argv[0], argc, 2, 3))
-		fputs("Wrong number of arguments for `disable'.\n"
-			"Try `service help disable' for more information.\n",
-			stderr);
 		return EXIT_FAILURE;
-	}
 
 	for (ptr = argv[1]; isalnum(*ptr) || *ptr == '_'; ++ptr)
 		;
 
 	if (*ptr != '\0') {
 		fprintf(stderr, "Invalid service name '%s'\n", argv[1]);
+		tell_read_help(argv[0]);
 		return EXIT_FAILURE;
 	}
 

servicecmd/enable.c

@@ -31,18 +31,15 @@ static int cmd_enable(int argc, char **argv)
 	int ret = EXIT_FAILURE;
 	struct stat sb;
 
-	if (argc < 2 || argc > 3) {
+	if (check_arguments(argv[0], argc, 2, 3))
-		fputs("Wrong number of arguments for `enable'.\n"
-			"Try `service help enable' for more information.\n",
-			stderr);
 		return EXIT_FAILURE;
-	}
 
 	for (ptr = argv[1]; isalnum(*ptr) || *ptr == '_'; ++ptr)
 		;
 
 	if (*ptr != '\0') {
 		fprintf(stderr, "Invalid service name '%s'\n", argv[1]);
+		tell_read_help(argv[0]);
 		return EXIT_FAILURE;
 	}
 

servicecmd/servicecmd.c

@@ -55,6 +55,23 @@ void usage(int status)
 	exit(status);
 }
 
+void tell_read_help(const char *cmd)
+{
+	fprintf(stderr, "Try `%s help %s' for more information.\n",
+		__progname, cmd);
+}
+
+int check_arguments(const char *cmd, int argc, int minc, int maxc)
+{
+	if (argc >= minc && argc <= maxc)
+		return 0;
+
+	fprintf(stderr, "Too %s arguments for `%s'\n",
+			argc > maxc ? "many" : "few", cmd);
+	tell_read_help(cmd);
+	return -1;
+}
+
 int main(int argc, char **argv)
 {
 	command_t *cmd;

servicecmd/servicecmd.h

@@ -60,6 +60,21 @@ extern command_t *commands;
 */
 void usage(int status) NORETURN;
 
+/*
+	Write a message to stderr that advises the user how to consult the
+	help text for a specific command.
+*/
+void tell_read_help(const char *cmd);
+
+/*
+	Check if the argument count is within specified bounds (minc and maxc
+	inclusive). If it is, return 0.
+
+	If it isn't, complain about a wrong number of arguments for a
+	command (cmd), tell the user to consult the help text and return -1.
+*/
+int check_arguments(const char *cmd, int argc, int minc, int maxc);
+
 /*
 	To implement a new command, add a global, static instance of a
 	command_t (or derived) structure to a C file and pass it to this