Perl for Web Site Management

Modifying HREF Attributes

We’re halfway there: we’ve modified all our filenames to be consistently lowercase and to end in .html. Now we just need to edit the HREF attributes of the links inside those HTML files to reflect those changes. To do that, we will need to write a new script that can open up each member of a list of files that is passed to it, make changes to that file, and save the changes back to disk.

Even more than the renaming-files example we just finished, this one exposes us to a real risk of accidentally doing bad things to our data. Again, please make sure you have a good backup before proceeding. Also, see Parsing HTML with Regexes Considered Harmful for a discussion of some of the limitations of the approach presented here.

Parsing HTML with Regexes Considered Harmful

The accompanying example shows how to use a simple regular expression to manipulate a collection of HTML files (specifically, to alter the HREF attributes in the files’ <A> tags). Although I think it’s a useful example (or I wouldn’t be presenting it here), you should be aware of the inherent limitations of this approach.

In short, regular expressions, for all their power, simply can’t do a good job of breaking down an HTML document into its component parts (a process called parsing). Among the things that are perfectly valid in an HTML document, but which tend to give simple regex-based parsers fits, are:

• Tags that continue across multiple lines

• Tag attributes that contain quoted angle brackets ...