title: I am using sed with a regex in Linux but not getting the expected answer
body: <p>I have a file in which the content looks like this</p>
  
  <pre><code>1234 Name Surname Address
  </code></pre>
  
  <p>and I should have an output file like this</p>
  
  <pre><code>(123) Name Surname Address
  </code></pre>
  
  <p>I am using the Linux <code>sed</code> command </p>
  
  <pre><code>sed -e 's/^\([0-9]\{3\}\)\./&amp;/g' file_name
  </code></pre>
  
  <p>But my command doesn't change the input file at all.</p>
  
  <p>Please help,</p>