title: How to change commit author for multiple commits using filter branch?
body: <p>I am using this script found at this <a href="https://help.github.com/en/articles/changing-author-info" rel="noreferrer">link</a> to edit author info across all commits.</p>
  
  <pre><code>#!/bin/sh
  
  git filter-branch --env-filter '
  
  OLD_EMAIL="your-old-email@example.com"
  CORRECT_NAME="Your Correct Name"
  CORRECT_EMAIL="your-correct-email@example.com"
  
  if [ "$GIT_COMMITTER_EMAIL" = "$OLD_EMAIL" ]
  then
      export GIT_COMMITTER_NAME="$CORRECT_NAME"
      export GIT_COMMITTER_EMAIL="$CORRECT_EMAIL"
  fi
  if [ "$GIT_AUTHOR_EMAIL" = "$OLD_EMAIL" ]
  then
      export GIT_AUTHOR_NAME="$CORRECT_NAME"
      export GIT_AUTHOR_EMAIL="$CORRECT_EMAIL"
  fi
  ' --tag-name-filter cat -- --branches --tags
  </code></pre>
  
  <p>However, I am getting the following error(warning?):</p>
  
  <pre><code>Cannot create a new backup.
  A previous backup already exists in refs/original/
  Force overwriting the backup with -f
  </code></pre>
  
  <p>I checked the log too. The author info didn't change. What am I doing wrong here? </p>
  
  <p><strong>Update:</strong> As mentioned by <a href="https://stackoverflow.com/users/6330106/elpiekay">@elpiekay</a>, the <code>-f</code> flag made the script work. </p>
  
  <p>But can anyone explain the error log itself?  Why does it mention about backup ? I never made any backup before (<em>unsure what backup is being referred in the error log</em>)</p>