I used this to tape together a
printURL command so I could pass in a filename and get its URL to pass to a command line executable that sends Webmentions. It surprised me that that wasn't somehow possible in the basic Jekyll install and that I couldn't find something that already did it--but it was much easier to write myself than I expected.
Though in the process, I discovered that Ruby library documentation sites error out a ton...
Comment with a webmention, or with commentpara.de