title: Unique File ID for Excel Files in R
body: <p>I want to import a list of excel files with a unique identifier into R.</p>
  <p>I thought of using File Name (basename(File)), however there is the potential of the file name changing and introducing duplicates into the data.</p>
  <p>Next option would be Created Time, but that comes with it's own issues.</p>
  <p>Is there a unique file ID for excel files that remains the same when moved and renamed? and can that ID be retrieved within R?</p>