字边界结束和边缘之间的正则表达式差异 [英] Regex difference between word boundary end and edge

问题描述

正则表达式 说

符号\<和 \> 分别匹配在一个词的开头和结尾.符号 \b 匹配空字符串一个字的边缘

The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word

(一个词的)结束和边缘有什么区别?

What is the difference between an end and an edge (of a word)?

推荐答案

\b 和 \</\> 的区别code> 是 \b 可用于 PCRE 正则表达式模式(当您指定 perl=TRUE 时)和 ICU 正则表达式模式(stringr 包).

The difference between the \b and \< / \> is that \b can be used in PCRE regex patterns (when you specify perl=TRUE) and ICU regex patterns (stringr package).

> s = "no where nowhere"
> sub("\\<no\\>", "", s)
[1] " where nowhere"
> sub("\\<no\\>", "", s, perl=T) ## \> and \< do not work with PCRE
[1] "no where nowhere"
> sub("\\bno\\b", "", s, perl=T) ## \b works with PCRE
[1] " where nowhere"

> library(stringr)
> str_replace(s, "\\bno\\b", "")
[1] " where nowhere"
> str_replace(s, "\\<no\\>", "")
[1] "no where nowhere"

\<(始终代表单词的开头)和 \>(始终匹配单词的结尾)的优点在于它们是明确的.\b 可以匹配两个位置.

The advantage of \< (always stands for the beginning of a word) and \> (always matches the end of a word) is that they are unambiguous. The \b may match both positions.

还有一件事要考虑(参考):

One more thing to consider (refrence):

gsub 和 gregexpr 的 POSIX 1003.2 模式对于重复的字边界(例如，pattern = "\b")无法正常工作.将 perl = TRUE 用于此类匹配(但对于非 ASCII 输入可能无法按预期工作，因为单词"的含义取决于系统).

POSIX 1003.2 mode of gsub and gregexpr does not work correctly with repeated word-boundaries (e.g., pattern = "\b"). Use perl = TRUE for such matches (but that may not work as expected with non-ASCII inputs, as the meaning of ‘word’ is system-dependent).

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