title: Parameterized RMarkdown File Name
body: <p>I am trying to use 1 parameterized RMarkdown file to run 3 reports and output a different file name for each report (e.g. Report_A.html, Report_B.html, Report_C.html).</p>
  
  <p>I have tried modifying the knit hook of the YAML, but am unable to get it to resolve the parameters.</p>
  
  <p>I do not want to create a separate R file to loop through the parameters.</p>
  
  <p>So far I have the following and the title is parameterized but the report name is Report_<code>r params$site</code>_2019-12-12.html</p>
  
  <pre><code>params:
    site: "A"
  title:  "Report `r params$site`"
  knit: (function(inputFile, encoding) {
        rmarkdown::render(inputFile,
        output_file=paste0("Report_", `r params$site`, "_", Sys.Date(),'.html')) })
  </code></pre>
  
  <p>Any suggestions would be appreciated - thank you!</p>