Add simple usage message for mirb

tools/mirb/mirb.c

@@ -132,6 +132,67 @@ is_code_block_open(struct mrb_parser_state *parser)
   return code_block_open;
 }
 
+void mrb_show_version(mrb_state *);
+void mrb_show_copyright(mrb_state *);
+
+struct _args {
+  int argc;
+  char** argv;
+};
+
+static void
+usage(const char *name)
+{
+  static const char *const usage_msg[] = {
+  "switches:",
+  "--version    print the version",
+  "--copyright  print the copyright",
+  NULL
+  };
+  const char *const *p = usage_msg;
+
+  printf("Usage: %s [switches]\n", name);
+  while(*p)
+    printf("  %s\n", *p++);
+}
+
+static int
+parse_args(mrb_state *mrb, int argc, char **argv, struct _args *args)
+{
+  static const struct _args args_zero = { 0 };
+
+  *args = args_zero;
+
+  for (argc--,argv++; argc > 0; argc--,argv++) {
+    char *item;
+    if (argv[0][0] != '-') break;
+
+    item = argv[0] + 1;
+    switch (*item++) {
+    case '-':
+      if (strcmp((*argv) + 2, "version") == 0) {
+        mrb_show_version(mrb);
+        exit(0);
+      }
+      else if (strcmp((*argv) + 2, "copyright") == 0) {
+        mrb_show_copyright(mrb);
+        exit(0);
+      }
+      else return -3;
+    default:
+      return -4;
+    }
+  }
+
+  return 0;
+}
+
+static void
+cleanup(mrb_state *mrb, struct _args *args)
+{
+  mrb_close(mrb);
+}
+
 /* Print a short remark for the user */
 static void
 print_hint(void)
@@ -154,7 +215,7 @@ print_cmdline(int code_block_open)
 }
 
 int
-main(void)
+main(int argc, char **argv)
 {
   char ruby_code[1024] = { 0 };
   char last_code_line[1024] = { 0 };
@@ -166,12 +227,11 @@ main(void)
   struct mrb_parser_state *parser;
   mrb_state *mrb;
   mrb_value result;
+  struct _args args;
   int n;
   int code_block_open = FALSE;
   int ai;
 
-  print_hint();
-
   /* new interpreter instance */
   mrb = mrb_open();
   if (mrb == NULL) {
@@ -179,6 +239,15 @@ main(void)
     return EXIT_FAILURE;
   }
 
+  n = parse_args(mrb, argc, argv, &args);
+  if (n < 0) {
+    cleanup(mrb, &args);
+    usage(argv[0]);
+    return n;
+  }
+
+  print_hint();
+
   cxt = mrbc_context_new(mrb);
   cxt->capture_errors = 1;