正则表达式锚点清单
^据说匹配行的开头，但它在"\n"之后不匹配，“\r”或“\r\n”。但它匹配字符串的开头。它在什么意义上匹配行的开头，它与\A有何不同？$据说匹配行尾，但它与"\n"之前不匹配，“\r”或“\r\n”。但它匹配字符串的结尾。它在什么意义上匹配行尾，它与\z有何不同？\Z与\z不同，如果位于字符串末尾，则匹配"\n"之前的位置。在我看来，\A和\z是自然配对的概念，而\Z是一个相当奇怪的概念。为什么\Z和\z按原样定义，而不是相反？而且，您什么时候想使用\Z？
你能用例子来说明上面的内容吗？ 如果语言/标准之间的差异很重要，那么列出它们会很有帮助。
^is said to match the beginning of a line, but it does not match right after a"\n","\r"or"\r\n". It matches the beginning of a string, though. In what sense does it match the beginning of a line, and how is it different from\A?$is said to match the end of a line, but it does not match right before a"\n","\r"or"\r\n". It matches the end of a string, though. In what sense does it match the end of a line, and how is it different from\z?\Z, unlike\z, matches right before"\n"if that is at the end of a string. It seems to me that\Aand\zare naturally paired concept, and\Zis rather an odd one. Why is it that\Zand\zare defined as is, and not the other way around? And, when would you want to use\Z?
Can you illustrate the above using examples?
If difference among languages/standards matters, it would be helpful to list them.
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不同之处在于
^和$锚点可以修改行为。启用
multiline模式后，^和$锚点断言行的开头和结尾。当
multiline模式关闭时，^和$锚点断言字符串的开头和结尾。大多数正则表达式实现都有
多行模式。对于 Ruby、Perl 或 Javascript，它是使用
m修饰符定义的。例如/pattern/m在 .NET 中，它是在模式本身内使用
(?m)定义的，或者从RegexOptions.Multiline枚举定义的。要回答你的第三个问题...
\A- 匹配必须出现在字符串的开头。\Z- 匹配必须出现在字符串末尾或字符串末尾的\n之前。\z- 匹配必须出现在字符串的末尾。这三个是不受任何修饰符影响的常量。我同意
\A和\z似乎是不合逻辑的配对。这对我来说也没有多大意义。但如果您可能希望忽略尾随换行符，那么\Z可能是首选。The difference is that the
^and$anchors can have modified behaviors.With
multilinemode on, the^and$anchors assert the beginning and end of a line.With
multilinemode off, the^and$anchors assert the beginning and end of the string.Most regex implementations have a
multilinemode.With Ruby, Perl, or Javascript, it's defined with the
mmodifier. e.g./pattern/mIn .NET it's defined with
(?m)inside the pattern itself, or from theRegexOptions.Multilineenumeration.To answer your 3rd question...
\A- The match must occur at the start of the string.\Z- The match must occur at the end of the string or before\nat the end of the string.\z- The match must occur at the end of the string.These three are constants that are not affected by any modifiers. I agree that
\Aand\zseem to be an illogical pairing. It doesn't make a great deal of sense to me either. But in a case where you may have a trailing line feed that you wish to ignore then\Zmight be preferred.