Back to the job: I want to observe what happens, so I take before and after shots with ls $paulm/inchoate/archives/00*.html; wc -l /etc/apache2/paulm.com-redirect.conf. I.e. take the before shot, run the above perl line, and re-run the ls; wc -l "after" shot. For the latter I get, reassuringly,

ls: /home/www/paulm/paulm.com/inchoate/archives/00*.html: No such file or directory

47 /etc/apache2/paulm.com-redirect.conf

Since this has changed my apache configs another webserver kick's needed.

And categories, monthly archives, RSS, and...?

It's all well changing the entries but what about the old-style archives/2004_08.html? Laziness prevailing here again I checked the last week's logs for references,

ls $paulm/inchoate/archives/200*_*.html # this revealed four from 2004, hence:
grep archives/2004_0 $logs

Nothing. Delete 'em: rm $paulm/inchoate/archive/200*_*.html

The same wasn't true for categories unfortunately,

grep cat_ $logs

The old RSS feeds could go, rm $paulm/inchoate/archives/[0-9]*.xml $paulm/inchoate/[0-9]*.xml

Correcting old links

My site's built from little XML fragments and full HTML pages, so I'm going to look in all of them and switch references to the old style,

find $paulm \( -name '*.html' -o -name '*.xml' \) | xargs grep -l 'inchoate/archives/00' | tee /tmp/old-style-pages

There were tantalisingly few there (about four)--I was sorely tempted to hand-edit them. But no, see if I can whip out another one-liner in less time than it takes to look each one up:

</tmp/old-style-pages xargs perl -pi~ -MFile::Slurp=read_file -le '

  BEGIN {

    %h = map { (split)[1 => 2] } read_file("/etc/apache2/paulm.com-redirect.conf");

    s~http://paulm.com~~ for values %h;

    $re=join "|", map "(?:http://paulm.com)?$_", keys %h 

  };

  s/($re)/$h{$1}/ge'

The neat trick here is that I'm doing an in-place file change while using the BEGIN clause to slurp in the redirect file and make a hash mapping the old style pages ("word" 1 of the line) to the new URL ("word" 2). Skipping the next line for a second I create a big regex to match any reference the old-style URLs.

Now those mystery references to http://paulm.com: This is quite subtle. The references in the script to my base URL http://paulm.com combine to remove that from the URLs in the pages. By not replacing with the full URL, the script also works on matches on filesystem references, e.g. /home/www/paulm/paulm.com/inchoate/archives/002918.html. Without it you'd end up with /home/www/paulm/paulm.comhttp://paulm.com/inchoate... (I didn't get this the first time round; only after I ran the script on one page and noticed it on a file that did an INCLUDE of a blog entry).

(By the way, if you're thinking, my god, who writes scripts like that off the top of his head? The answer is, if you're prepared to experiment, play, and believe it's possible: "you")

What next?

The test for success here is no 404s (missing pages), just 301s (permanent redirects). So over the next few days I'll be keeping an eye on my server logs using techniques shown above, and tail -f the error log in a window.

Moral

Changing one's URL scheme is not something to be undertaken lightly! However, if you do choose to, having a blogging engine that enables relatively straightforward construction of scripts and one-liners to manipulate its data renders the job a matter of a half-hour or so of reading docs and experimentation.

And of course behold the power of perl and unix to perform sophisticated data transformations and get the job done!