Chapter 2. Parsing Techniques

One thing Perl is particularly good at is throwing data around. There are two types of data in the world: regular, structured data and everything else. The good news is that regular data—colon delimited, tab delimited, and fixed-width files—is really easy to parse with Perl. We won't deal with that here. The bad news is that regular, structured data is the minority.

If the data isn't regular, then we need more advanced techniques to parse it. There are two major types of parser for this kind of less predictable data. The first is a bottom-up parser. Let's say we have an HTML page. We can split the data up into meaningful chunks or tokens—tags and the data between tags, for instance—and then reconstruct what each token means. See Figure 2-1. This approach is called bottom-up parsing because it starts with the data and works toward a parse.