Migrating from Drupal 6 to Nikola

(I recorded an episode for Hacker Public Radio about this subject, which will be 'on air' on 2014-09-30. HPR1507)

As promised, some details about how I migrated my blog from Drupal 6 to Nikola.

First of all some details about the Drupal site I migrated from.

  • I did not have node revisions on my Drupal site.
  • My Drupal site had one 'vocabulary', which was used to assign tags to each post.
  • I did not use page aliases, so every post I had, had an url like johanv.org/node/195.

Also worth mentioning is that I used pandoc 1.12.3.3 to convert the html of my nodes to RestructuredText, the format that Nikola uses by default. If you have another version of pandoc installed, you will possibly need to tweak the script I used.

I created a new subdomain for my blog: blog.johanv.org. I used a script that creates a blog post for every published Drupal node on my Drupal site.

This script was created with a lot of trial and error. It can probably use some improvements, so I invite you to look at it, and to send me pull requests

#!/bin/bash

# migrate articles and stories from drupal 6 to nikola
# Copyright 2014 Johan Vervloet
# You can use and distribute this script under the terms of the
# GNU General Public License version 3 or later.

# Notes:
#  * my drupal site has no multiple revisions of posts.
#  * I had one vocabulary that I used for tagging posts.
#  * you need to have pandoc installed for this script to work.


# please change the two variables below
# according to your needs

# mysql command to connect to your drupal database
MYSQL_CMD="mysql -N -s -u root johanv6"
# directory to save the files
OUT_DIR="/tmp/out"

mkdir -p $OUT_DIR

nodes=$(echo "
      SELECT nid
      FROM node
      WHERE status > 0
      " | $MYSQL_CMD);

for nid in $nodes
do
      out_file=$OUT_DIR/$nid.rst

      details=$(echo "
              SELECT FROM_UNIXTIME(created),title
              FROM node
              WHERE nid=$nid
              " | $MYSQL_CMD | sed 's/\t/;/g');

      created=`echo $details | cut -f 1 -d\;`
      title=`echo $details | cut -f 2 -d\;`

      tags=$(echo "
              SELECT GROUP_CONCAT(td.name)
              FROM term_node tn JOIN term_data td ON tn.tid=td.tid
              WHERE tn.nid=$nid
              " | $MYSQL_CMD);

      cat > $out_file << EOF
.. title: $title
.. slug: node-$nid
.. date: $created
.. tags: $tags
.. link:
.. description:
.. type: text

EOF


      echo "SELECT body FROM node_revisions WHERE nid=$nid" | \
      $MYSQL_CMD | \
# convert node from html to rst
      pandoc --from=html --to=rst | \
# some trial and error for newlines
      sed 's/\\\\n/\n/g' | \
# convert references to other posts
      perl -p -000 -e 's;`((\s|[^<])*)</node/([0-9]*)>`__;:doc:`\1<node-\3>`;g' | \
# lots of trial and error to convert inline code
        perl -p -000 -e 's/``([^`]*\\n[^`]*)``/\n\n::\n\n\1\n\n/g' | \
      sed 's/\\n/\n  /g' | sed 's/\\t/\t/g' | sed 's/\\ / /g' | \
# convert video-links to youtube-links
# I did the conversion of \_ to _ manually
      sed 's/\[video:.*[/=]\([^/=]*\)\]/.. youtube:: \1/g' >> $out_file

# some output to show progress
      echo -n .

done

The script queries the database of the Drupal instance, to do the following for each node:

  • get the timestamp, title and tags for the node.
  • create a rst document with this metadata.
  • do a lot of manipulations on the node content, and add the content to the rst document.

Those manipluations are the following

  • conversion from html to restructured text (rst)
  • fixing line ending issues
  • conversion of references to other blog posts
  • handling issues with blocks with literal code in the blog posts
  • conversion of links to youtube videos

I won't read out the whole script, that wouldn't make interesting radio, but I will put a link in the shownotes. It's an ugly script: you'll have to edit the first lines, describing how you can connect to the database (put your credentials in my.cnf), and where the output files should go. (By default they go in /tmp/out.)

You probably have to tweak the script to adapt it to your needs, but hey, you have a starting point.

The script converts each node e.g. johanv.org/node/195 to a blog post blog.johanv.org/posts/node-195.html. This way I could easily convert hyperlinks to other posts to the corresponding html page of the new blog.

On the location of my old blog, I put an .htaccess file, that redirects all requests /node/number to the correct page on the new blog

RewriteEngine On
RewriteCond %{HTTP_HOST} !^blog\.
RewriteRule ^(.*)node/(.*)$ http://blog.johanv.org/posts/node-$2 [R=301,L]
RewriteRule ^(.*)$ http://blog.johanv.org/$1 [R=301,L]

You will have to With the combination of the script and the .htaccess file, 90% of the migration was very easy. But - as always - the remaining 10% needs some manual work. Like e.g. converting the youtube links containing underscores. Those underscores were prefixed with a backslash, which wasn't correct. Because there weren't too many of those errors, I fixed them manually.

Another thing you should do manually, is migrating attachments and images to your new site. Let's hope you don't have too many of them. And if so, you can probably write a script as well.

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