title: autopep8 in a git pre-commit -- how to automatically recommit?
body: <p>I have a git pre-commit hook that runs <code>autopep8</code> on touch python files.  My problem with it is that:
  <code># If there are whitespace errors,</code>it <code>print</code>s<code>the offending file names and fail</code>s<code>.</code> (see below.)</p>
  
  <p>Question:</p>
  
  <p><strong>How do I make it re-add and re-commit the files that I currently have to fix manually?</strong></p>
  
  <p>Thanks!</p>
  
  <pre><code>#!/bin/bash
  
  
  #
  # An example hook script to verify what is about to be committed.
  # Called by "git commit" with no arguments.  The hook should
  # exit with non-zero status after issuing an appropriate message if
  # it wants to stop the commit.
  #
  # To enable this hook, rename this file to "pre-commit".
  
  if git rev-parse --verify HEAD &gt;/dev/null 2&gt;&amp;1
  then
      against=HEAD
  else
      # Initial commit: diff against an empty tree object
      against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
  fi
  
  # If you want to allow non-ascii filenames set this variable to true.
  allownonascii=$(git config hooks.allownonascii || echo false)
  
  # Redirect output to stderr.
  exec 1&gt;&amp;2
  
  # Cross platform projects tend to avoid non-ascii filenames; prevent
  # them from being added to the repository. We exploit the fact that the
  # printable range starts at the space character and ends with tilde.
  if [ "$allownonascii" != "true" ] &amp;&amp;
      # Note that the use of brackets around a tr range is ok here, (it's
      # even required, for portability to Solaris 10's /usr/bin/tr), since
      # the square bracket bytes happen to fall in the designated range.
      test $(git diff --cached --name-only --diff-filter=A -z $against |
        LC_ALL=C tr -d '[ -~]\0' | wc -c) != 0
  then
      echo "Error: Attempt to add a non-ascii file name."
      echo
      echo "This can cause problems if you want to work"
      echo "with people on other platforms."
      echo
      echo "To be portable it is advisable to rename the file ..."
      echo
      echo "If you know what you are doing you can disable this"
      echo "check using:"
      echo
      echo "  git config hooks.allownonascii true"
      echo
      exit 1
  fi
  
  # If there are whitespace errors, print the offending file names and fail.
  git diff-index --check --cached $against --
  
  touched_python_files=`git diff --cached --name-only |egrep '\.py$' || true`
  if [ -n "$touched_python_files" ]; then
      autopep8 \
          --ignore=E26 \
          --in-place \
          --jobs=0 \
          --max-line-length=150 \
          $touched_python_files
  fi
  </code></pre>