Read stdin if no argument supplied

nsh.c

@@ -210,25 +210,26 @@ void highlight_include(const char *line, int *i)
 	}
 }
 
-/* Main function to process input */
-int main(int argc, char **argv)
+void highlight(char *filename)
 {
-	if (argc < 2) {
-		fprintf(stderr, "nsh <file> <file2> ...\n");
-		exit(1);
-	}
-	for (int i = 1; i < argc; i++) {
-		FILE *f = fopen(argv[i], "r");
+	char *ext;
+	FILE *f;
+	if (filename == NULL) {
+		f = stdin;
+	} else {
+		f = fopen(filename, "r");
 		if (!f) {
-			fprintf(stderr, "Unable to open file: %s\n", argv[i]);
+			fprintf(stderr, "Unable to open file: %s\n", filename);
 			exit(1);
 		}
 		/* Handle file without extension */
-		char *ext = strrchr(argv[i], '.');
+		ext = strrchr(filename, '.');
 		if (ext != NULL) {
 			/* How to identify file type if there isn't extension? */
 			ext++;
 		}
+	}
+
 	char buffer[1024];
 	char word[256];
 	int word_len = 0;
@@ -336,6 +337,18 @@ int main(int argc, char **argv)
 			}
 		}
 	}
+
+}
+
+/* Main function to process input */
+int main(int argc, char **argv)
+{
+	if (argc > 1) {
+		for (int i = 1; i < argc; i++) {
+			highlight(argv[i]);
+		}
+	} else {
+		highlight(NULL);
 	}
 	return 0;
 }