什么是仅匹配空字符串的正则表达式? [英] What is a regex to match ONLY an empty string?

问题描述

有很多关于正则表达式匹配潜在空字符串的帖子，但我找不到任何提供仅匹配空字符串的正则表达式的帖子.

There are lots of posts about regexs to match a potentially empty string, but I couldn't readily find any which provided a regex which only matched an empty string.

我知道 ^ 将匹配任何行的开头，而 $ 将匹配任何行的结尾以及字符串的结尾.因此，/^$/ 比\n"、foobar\n\n"等空字符串匹配的多.

I know that ^ will match the beginning of any line and $ will match the end of any line as well as the end of the string. As such, /^$/ matches far more than the empty string such as "\n", "foobar\n\n", etc.

不过，我会认为 /\A\Z/ 只会匹配空字符串，因为 \A 匹配字符串的开头和 \Z 匹配字符串的结尾.但是，我的测试表明 /\A\Z/ 也将匹配\n".这是为什么?

I would have thought, though, that /\A\Z/ would match just the empty string, since \A matches the beginning of the string and \Z matches the end of the string. However, my testing shows that /\A\Z/ will also match "\n". Why is that?

推荐答案

如 http://www.regular-expressions.info/anchors.html 在以换行符结尾的字符串"部分下，\Z 通常会在字符串中的最后一个换行符结束之前匹配以换行符结尾.如果只想匹配字符串的结尾，则需要使用\z.此规则的例外是 Python.

As explained in http://www.regular-expressions.info/anchors.html under the section "Strings Ending with a Line Break", \Z will generally match before the end of the last newline in strings that end in a newline. If you want to only match the end of the string, you need to use \z. The exception to this rule is Python.

换句话说，要独占匹配一个空字符串，您需要使用/\A\z/.

In other words, to exclusively match an empty string, you need to use /\A\z/.

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