tybg: make tybg without argument display the default wallpaper

The ty* tools need some love…

src/bin/tybg.c

@@ -10,15 +10,23 @@ main(int argc, char **argv)
    int i, perm = 0;
    
    if (!getenv("TERMINOLOGY")) return 0;
-   if (argc <= 1)
+   if (argc > 1 &&
+       (!strcmp(argv[1], "-h") || !strcmp(argv[1], "--help")))
      {
-        printf("Usage: %s [-p] FILE1 [FILE2 ...]\n"
+        printf("Usage: %s [-p] [FILE1 FILE2 ...]\n"
                "  Change the terminal background to the given file/uri\n"
                "  -p  Make change permanent (stored in config)\n"
                "\n",
                argv[0]);
         return 0;
      }
+   if (argc <= 1)
+     {
+        char tbuf[32];
+          snprintf(tbuf, sizeof(tbuf), "%c}bt", 0x1b);
+        if (write(0, tbuf, strlen(tbuf) + 1) != (signed)(strlen(tbuf) + 1)) perror("write");
+        return 0;
+     }
    for (i = 1; i < argc; i++)
      {
         char *path, buf[PATH_MAX * 2], tbuf[PATH_MAX * 3];