dwm/patch/bar_layoutmenu.c

void
layoutmenu(const Arg *arg) {
	FILE *p;
	char c[3], *s;
	int i;

	if (!(p = popen(layoutmenu_cmd, "r")))
		 return;
	s = fgets(c, sizeof(c), p);
	pclose(p);

	if (!s || *s == '\0' || c[0] == '\0')
		 return;

	i = atoi(c);
	setlayout(&((Arg) { .v = &layouts[i] }));
}