为什么默认情况下正则表达式会贪婪? [英] Why are regular expressions greedy by default?

问题描述

对于初学者编写正则表达式，这似乎是一个巨大的困惑源，它可能导致隐藏的性能问题，而且似乎典型的用例是非贪婪的.

It seems that this is a huge source of confusion for beginners writing regular expressions, can cause hidden performance problems, and it would seem that a typical use case would be non-greedy.

这是仅出于遗留原因(它是如何首先完成的，每个实现都对此进行复制)，还是有原因?

Is this just for legacy reasons (it was how it was first done, and every implementation copies that), or is there a reason for it?

推荐答案

歇斯底里的葡萄干

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答案的一部分可能涉及实际计算中RE的起源.它们最初是从自动机理论和形式语言理论开始的理论概念，直到 ed( 1).

Hysterical Raisens

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Part of the answer may involve the origins of REs in practical computing. They were originally a theoretical concept from automata theory and formal language theory until Ken Thompson himself wrote a real implementation and used them in qed and ed(1).

原始版本只有贪婪的语法，因此甚至没有决定.

The original version had only the greedy syntax and so there wasn't a decision to even make.

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