====== completely remove a file from all revisions ======
If you've added a file to a .gitignore list and it still shows up for commits, you can ignore it from that point on by removing it with this:
<code>
git rm --cached <file>
</code>

If you find a file that should never have been committed into the repo, you need to do more than this.  Adding the file to a .gitignore list doesn't get rid of it for you, and you want the file to disappear from everything.  (probably a good idea to back up repo before doing this)

**method 1**
<code>
git filter-branch --index-filter 'git rm --cached <file>' HEAD
</code>

**method 2**
<code>
git filter-branch -f --index-filter 'git update-index --remove filename' HEAD
</code>

===== External Links =====
  * http://www.gitready.com/beginner/2009/03/06/ignoring-doesnt-remove-a-file.html
  * http://github.com/guides/completely-remove-a-file-from-all-revisions