It’s possible with native messaging. You write a content script that injects some JavaScript to check the page that then messages with background page that then

It’s possible with native messaging. You write a content script that injects some JavaScript to check the page that then messages with background page that then messages an external application. Though I likely would make it a page action or a context menu action. I think if you’re on OS X that it would be easier to write a small automater action that you register as a service that after you select some text and right click it it parses the text and calls the shell command.