title: Excel formula how to concatenate string for external reference
body: <p>Say I have the following formula in a cell that reads the value of a cell from another work book</p>
  
  <pre><code>='c:\temp\[external book.xlsx]SheetX'!$E$4
  </code></pre>
  
  <p>and I want the value of <code>c:\temp\[external book.xlsx]SheetX</code> to come from another cell in this sheet. How would I rewrite this formula to concatenate this value and <code>"!$E$4"</code></p>
  
  <p>Lets say the cell <code>A1</code> contains <code>c:\temp\[external book.xlsx]SheetX</code></p>