I finally became reasonable and admitted to myself that there is no point in maintaining two separate blogs about Computing, this one and one on digital art, especially if the latter had so few updates. I hence looked for a way to transfer all the content from that blog to this one. A quick search returned a post by one of the WordPress developers, with the gist of the solution: just use the built-in export/import functionality to save all posts, pages, comments, categories and tags from the blog to be deleted and then load them into the blog to be kept.
Of course, if you have added lots of widgets to and customized the theme of your retired blog, all that will be lost, and you will have to decide whether and how to change the look and feel of the kept blog in order to accommodate the content of the retired blog. No automation can help you in that… However, I’d expect links and their categories to also be exported, but they aren’t. Hence, if you have lots of links and blogrolls on your sidebars, I have no clue how to easily copy them to another blog. Fortunately, that was not the case with my digital art blog to be retired; a simple transfer of posts (and their comments, categories and tags) was all I needed.
I was pleasently surprised when the import process offered to also get the files uploaded to the retired blog. Since it used some Java applets, this would be really useful. Unfortunately, I got error messages saying ‘unknown file extension’: apparently only certain file attachments can be imported. Oh well, no big problem. I logged into my web hosting service, where I keep all my blogs in separate sub-folders, and used the cPanel file manager to move all uploaded files from one blog’s folder to the other, and then delete the retired blog’s folder. Back to the main cPanel view, I used the Manage redirects functionality in the Domains sub-panel, in order to make all URLs of the form http://michel.wermelinger.ws/digitar-te (the retired blog) redirect to http://michel.wermelinger.ws/chezmichel (this blog). Since I use the same permalink format in both blogs, namely year/month/post-title, any links to my retired blog will correctly resolve to the corresponding posts or files in this blog.
To sum up, the export/import facilities of WordPress go a long way to help the merging of blogs, but be prepared to do quite some manual tweaking, especially if the two blogs are very dissimilar in the presentation of their content. Among the things to consider are the merging of different permalink structures, ‘About’ pages, and blogrolls.