title: grep returns "<regular expression>" No such file or directory
body: <p>I have the following regular expression to match a phone number. The regular expression works <code>(123)123-123</code>, but I am puzzled by the last result.</p>
  
  <pre><code>user@host: grep -l -v -f *.txt -E "(\d{3})-\d{3}-\d{3}"
  f2.txt
  f3.txt
  f4.txt
  grep: (\d{3})-\d{3}-\d{3}: No such file or directory
  </code></pre>
  
  <p>Why is <code>grep</code> searching the regular expression?</p>
  
  <p>Here is the <code>ls</code>:</p>
  
  <pre><code>user@host:/tmp# ls
  f1.txt  f2.txt  f3.txt  f4.txt  
  </code></pre>