3Overview of Regular Expression Features and Flavors

Now that you have a feel for regular expressions and a few diverse tools that use them, you might think we’re ready to dive into using them wherever they’re found. But even a simple comparison among the egrep versions of the first chapter and the Perl and Java in the previous chapter shows that regular expressions and the way they’re used can vary wildly from tool to tool.

When looking at regular expressions in the context of their host language or tool, there are three broad issues to consider:

• What metacharacters are supported, and their meaning. Often called the regex “flavor.”

• How regular expressions “interface” with the language or tool, such as how to specify regular-expression operations, what operations are allowed, and what text they operate on.

• How the regular-expression engine actually goes about applying a regular expression to some text. The method that the language or tool designer uses to implement the regular-expression engine has a strong influence on the results one might expect from any given regular expression.

Regular Expressions and Cars

The considerations just listed parallel the way one might think while shopping for a car. With regular expressions, the metacharacters are the first thing you notice, just as with a car it’s the body shape, shine, and nifty features like a CD player and leather seats. These are the types of things you’ll find splashed across the pages of a glossy brochure, and a list ...

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