title: Vim: change prompt on shell escape
body: <p>I often use <code>:sh</code> while editing a file in vim so that I can perform small tasks like git commits before getting back to editing the file. However, sometimes I get confused whether my shell was started by my terminal emulator or it was started as a vim subshell, so typing <code>exit</code> at the prompt always runs the risk of closing the terminal emulator by accident rather than going back to my vim editing session. Is there a way to have vim modify my prompt, perhaps by the <code>$PS1</code> environment variable, when I start a shell from vim so that I know whether I'm in a subshell started by vim or not?</p>