title: comand cat ${i} doesn't read the file that i need
body: <p>I am trying to read some files using <code>cat ${i}</code> with <code>i</code> being 1 through n(basically I dont know how many files I will have) but it doesn't work. 
  Any ideas why?</p>
  
  <p>ex1:</p>
  
  <pre><code>cat ${1}   #works
  </code></pre>
  
  <p>ex2:</p>
  
  <pre><code>i=1
  cat ${i}   #doesnt work
  </code></pre>