As with anything that becomes popular in the IT industry, regular expressions come in many different implementations, with varying degrees of compatibility. This has resulted in many different regular expression flavors that don’t always act the same way, or work at all, on a particular regular expression.
Many books do mention that there are different flavors and point out some of the differences. But they often leave out certain flavors here and there—particularly when a flavor lacks certain features—instead of providing alternative solutions or workarounds. This is frustrating when you have to work with different regular expression flavors in different applications or programming languages.
Casual statements in the literature, such as “everybody uses Perl-style regular expressions now,” unfortunately trivialize a wide range of incompatibilities. Even “Perl-style” packages have important differences, and meanwhile Perl continues to evolve. Oversimplified impressions can lead programmers to spend half an hour or so fruitlessly running the debugger instead of checking the details of their regular expression implementation. Even when they discover that some feature they were depending on is not present, they don’t always know how to work around it.
This book is the first book on the market that discusses the most popular and feature-rich regular expression flavors side by side, and does so consistently throughout the book.
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