title: R Shiny error: could not find function "shell"
body: <p>My Shiny app works fine locally, but when I deploy it on shinyapps.io, I face the following error:</p>
  
  <p><code>Error: could not find function "shell"</code></p>
  
  <p>However, <a href="http://www.astrostatistics.psu.edu/datasets/R/html/base/html/shell.html" rel="nofollow noreferrer">shell</a> is an R built-in function (<code>base</code> package). So I don't really see what causes the error here and how to fix it?</p>
  
  <p>Please see follow-up question <a href="https://stackoverflow.com/questions/36431465/running-exe-from-r-status-127-warning-on-linux-not-on-windows">here</a></p>