title: insert a double backslash using sed
body: <p>I want to insert the line </p>
  
  <pre><code>text \\
  </code></pre>
  
  <p>into a file via sed. For one backslash to be inserted I would use three backslashes in the command. But escaping does not work for two backslashes:</p>
  
  <pre><code>sed -i 'text \\\\\\' $file
  </code></pre>
  
  <p>gives the following error:</p>
  
  <pre><code>sed: -e expression #1, char 57: unknown command: `
  '
  </code></pre>