Execute a command from a buffer

Question

Say, you create a new buffer (Fundamental), type a shell command and want it executed. Like you can do in a *scratch* buffer with lisp code (C-x C-e). Or you have a text file, that has text interspersed with shell commands. Or a shell script, and you want to execute one of the commands. Is there a way?

Or maybe you have an url in a buffer, and you want to do xdg-open URL. Or a path to a directory, and you want ls DIR. Is this possible? Maybe, like, M-! xdg-open , and then somehow paste the url into the minibuffer?