不以exp结尾的负Lookbehind表达式:'\ w +(?<！exp)\ b'或'\ w + \ b(?<！exp)' [英] Negative Lookbehind expression for not ending with exp : '\w+(?<!exp)\b' or '\w+\b(?<!exp)'

问题描述

对于表达式(?<!foo)，Negative Lookbehind断言，字符串中当前位置的紧前面不是foo.
现在要匹配不以字符abc结尾的字符串.
形式表达式是\w+(?<!abc)\b或\b\w+(?<!abc)\b.

For expression (?<!foo),Negative Lookbehind ,asserts that what immediately precedes the current position in the string is not foo.
Now to match string not ending with characters abc.
The formal expression is \w+(?<!abc)\b or \b\w+(?<!abc)\b.

echo "xxabc jkl" | grep -oP  '\w+(?<!abc)\b'
jkl

让我们尝试另一种形式:\w+\b(?<!abc).

Let's try another form: \w+\b(?<!abc).

echo "xxabc jkl" | grep -oP  '\w+\b(?<!abc)'
jkl

它也得到正确的答案.
在我看来，\w+\b(?<!abc)不是负向后看，也不在(?<!abc)后面，也不能称为负向后看.
1. \w+\b(?<!abc)表达式是否为负向后看?
2.为什么\w+\b(?<!abc)与\w+(?<!abc)\b具有相同的效果?

It get correct answer too.
In my opinion, \w+\b(?<!abc) is not a Negative Lookbehind,nothing behind (?<!abc),it can't called Negative Lookbehind.
1.Is expression \w+\b(?<!abc) a Negative Lookbehind?
2.Why \w+\b(?<!abc) has the same effct as \w+(?<!abc)\b?

推荐答案

1)这是一个否定的回溯窗口.如果您想匹配其他项目未进行的操作，则使用负向回溯. ?<!abc是否定后退窗口.因此，仅当进行中的标记不是不是"abc"时才是正确的，这与提供的字符串是正确的:"xxabc jkl"从技术上讲，空格在进行中"jkl"因此匹配.

1)It is a negative lookback window. Negative lookback is used if you want to match something not proceeded by something else. ?<!abc is a negative look back window. So it will only be true if the proceeding tokens are not "abc" which is true with the string provided: "xxabc jkl" technically, a space is proceeding "jkl" Therefore it matches.

2)\b查找单词边界.单词边界适用于两个正则表达式中都存在的空格和字符串结尾.如果您确实希望看到差异，请尝试从输入中删除空格.所以 使用"xxabcjkl"

2) \b looks for a word boundary. Word boundaries apply for spaces and end of strings which are present in both of your regular expressions. If you really want to see a difference, try taking the space out of the input. So use "xxabcjkl"

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