public static boolean isURL(String str) {
		try {
			URI uri = new URI(str);
			String s = uri.getScheme();
			return s != null && (s.equals("https") || s.equals("http") || s.equals("file"));
		} catch (URISyntaxException e) {
			return false;
		}
	}
Runs the given command + arguments and returns its output (both stdout and
stderr) as a string

@param cmd The command to execute
@return The output of the command or null if anything went wrong
src/main/java/dev/jbang/util/Util.java