PHP正则表达式非捕获非匹配组 [英] PHP regex non-capture non-match group

问题描述

我正在与正则表达式进行日期匹配，这一切都很顺利，我已经到目前为止：

 /（？：[0-3]）？[0-9]  - （？：[0-1]）？[0-9]  - （?:20）[0-1] [0-9] /
  

（希望）匹配单数或双位数字的数字和数字，双数或四位数二十一世纪的岁月。一些尝试和错误让我得到了这个结果。

但是，我有两个关于这些结果的简单问题：

1. （?:）这是一个简单的解释？显然这是一个非匹配的组。但是...然后...




2. 尾随的？是什么？例如（？）？

解决方案

这是一个评论和答案。

答案部分...我同意亚历克斯早期的答案。

1. <$ c $与（）相反，c>（?:）用于避免捕获文本，通常会引用较少的后缀与你想要的或提高速度表现。




2. 遵循（?:） - 或以下任何东西，除了 * +？或 } - 表示在合法比赛中可能找到或可能找不到上述项目。例如， / z34？/ 将匹配z3以及z34，但不匹配z35或z等。

评论部分...我做了可能被认为是对正在工作的正则表达式的改进：

<$ （0？[1-9] | [1-2] [0-9] | 30 | 31） - （0？[1- 9] | 10 | 11 | 12） - （（？：20）？[0-9] [0-9]）（？：\s | $）
pre>

- 首先，它避免了像0-0-2011这样的东西

- 其次，它避免像233443-4-201154564这样的东西

- 第三，它包括1-1-2022这样的东西

- 第四，它包括诸如1-1-11之类的东西

- 第五，它避免了像34-4-11这样的东西。

- 第六，它允许你捕获日，月和年，所以你可以更容易地在代码..代码中引用这些代码，例如，进一步检查（第二次捕获组2，并且是第一个捕获组29，这是闰年，否则第一个捕获组<29），以查看是否一个feb 29日期是否合格。

最后，请注意，您仍然会收到不存在的日期，例如31-6-11。如果你想避免这些，请尝试：

 （？：^ | \s）（？:(？ 0？[1-9] | [1-2] [0-9] | 30 | 31） - （0？[1078] | 10 | 12））|（？:( 0？[1-9] 1-2] [0-9] | 30） - （0？[469] | 11））|（？:( 0？[1-9] | [1-2] [0-9]） - （0 （2））） - （（？：20）？[0-9] [0-9]）（？：\s | $）
  

此外，我假设日期将在之前和后面跟着一个空格（或乞讨/行尾），但是您可能需要调整（例如，允许标点符号）。

其他引用此资源的评论者可能会发现有用的：
http://rubular.com/

I'm making a date matching regex, and it's all going pretty well, I've got this so far:

"/(?:[0-3])?[0-9]-(?:[0-1])?[0-9]-(?:20)[0-1][0-9]/"

It will (hopefully) match single or double digit days and months, and double or quadruple digit years in the 21st century. A few trials and errors have gotten me this far.

But, I've got two simple questions regarding these results:

1. (?: ) what is a simple explanation for this? Apparently it's a non-matching group. But then...

2. What is the trailing ? for? e.g. (? )?

解决方案

[Edited (again) to improve formatting and fix the intro.]

This is a comment and an answer.

The answer part... I do agree with alex' earlier answer.

1. (?: ), in contrast to ( ), is used to avoid capturing text, generally so as to have fewer back references thrown in with those you do want or to improve speed performance.

2. The ? following the (?: ) -- or when following anything except * + ? or {} -- means that the preceding item may or may not be found within a legitimate match. Eg, /z34?/ will match z3 as well as z34 but it won't match z35 or z etc.

The comment part... I made what might considered to be improvements to the regex you were working on:

(?:^|\s)(0?[1-9]|[1-2][0-9]|30|31)-(0?[1-9]|10|11|12)-((?:20)?[0-9][0-9])(?:\s|$)

-- First, it avoids things like 0-0-2011

-- Second, it avoids things like 233443-4-201154564

-- Third, it includes things like 1-1-2022

-- Forth, it includes things like 1-1-11

-- Fifth, it avoids things like 34-4-11

-- Sixth, it allows you to capture the day, month, and year so you can refer to these more easily in code.. code that would, for example, do a further check (is the second captured group 2 and is either the first captured group 29 and this a leap year or else the first captured group is <29) in order to see if a feb 29 date qualified or not.

Finally, note that you'll still get dates that won't exist, eg, 31-6-11. If you want to avoid these, then try:

(?:^|\s)(?:(?:(0?[1-9]|[1-2][0-9]|30|31)-(0?[13578]|10|12))|(?:(0?[1-9]|[1-2][0-9]|30)-(0?[469]|11))|(?:(0?[1-9]|[1-2][0-9])-(0?2)))-((?:20)?[0-9][0-9])(?:\s|$)

Also, I assumed the dates would be preceded and followed by a space (or beg/end of line), but you may want ot adjust that (eg, to allow punctuations).

A commenter elsewhere referenced this resource which you might find useful: http://rubular.com/

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