title: preventing a chunk run in rmarkdown
body: <p>I am using <code>Rmarkdown</code> and  <code>Knitr</code> using Rstudio. </p>
  
  <p>The following both print script and output to html. </p>
  
  <pre><code>```{r}
  summary(cars)
  ```
  </code></pre>
  
  <p>However the following will only print the output, that is embedded plot. </p>
  
  <pre><code>```{r, echo=FALSE}
  plot(cars)
  ```
  </code></pre>
  
  <p>I have situation different than above, I want to present the script but should not run in html as this will take very long time (hours if not days) to run. So I just did was put comment sign.</p>
  
  <pre><code>```{r}
  #summary(cars)
  ```
  </code></pre>
  
  <p>But I need a better way to do this - Is there any better way presenting script without running it. </p>