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3. Understanding Regular Expression Syntax > 3.1. That’s an Expression

That’s an Expression

You are probably familiar with the kinds of expressions that a calculator interprets. Look at the following arithmetic expression:

2 + 4

“Two plus four” consists of several constants or literal values and an operator. A calculator program must recognize, for instance, that “2” is a numeric constant and that the plus sign represents an operator, not to be interpreted as the “+” character.

An expression tells the computer how to produce a result. Although it is the result of “two plus four” that we really want, we don’t simply tell the computer to return a six. We instruct the computer to evaluate the expression and return a value.

An expression can be more complicated than “2 + 4”; in fact, it might consist of multiple simple expressions, such as the following:


  

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