Google RE2正则表达式转义期和下划线错误 [英] Google RE2 Regex Escaping periods and underscores error

问题描述

我正在尝试验证具有以下特征的username字符串:

• 不是以.或_
开头
• 不以.
结尾
• 不允许连续两个.
• 仅小写的letter characters和numbers

我的代码是username.matches('^(?!\.)(?!_)(?!.*\.$)(?!.*?\.\.)[a-z0-9_.]+$')

在线使用正则表达式模拟器可以正常工作

https://regex101.com/r/bDXMg3/2/

但是在 Google RE2语法中使用相同的语法(用于 Firestore安全规则)抛出大量错误

我试图将每个.

都转义两次

使用代码username.matches('^(?!\\.)(?!_)(?!.*\\.$)(?!.*?\\.\\.)[a-z0-9_.]+$')

它仅显示一个错误(开头为红色^符号)，但随后出现以下错误

Invalid regular expression pattern. Pattern: ^(?!\.)(?!_)(?!.*\.$)(?!.*?\.\.)[a-z0-9_.]+$.

谁能让我知道我在做什么错?

解决方案

RE2不支持先行(也不先行).

但是，该模式可以在没有环视的情况下进行重写:

^[a-z0-9][a-z0-9_]*([.][a-z0-9_]+)*$

详细信息

• ^-字符串开头
• [a-z0-9]-字母或数字
• [a-z0-9_]*-零个或多个小写字母，数字或下划线
• ([.][a-z0-9_]+)*-零个或多个序列
  • [.]-点
  • [a-z0-9_]+-一个或多个小写字母，数字或下划线
• $-字符串结尾.

I'm trying to validate a username string with the following characteristics:

• Not start with a . or _
• Not end with a .
• Don't allow two . in a row
• Only lowercase letter characters and numbers

my code is username.matches('^(?!\.)(?!_)(?!.*\.$)(?!.*?\.\.)[a-z0-9_.]+$')

Using a regex simulator online it's working

https://regex101.com/r/bDXMg3/2/

But using the same syntax in Google RE2 Syntax (used in Firestore Security Rules) is throwing a ton of errors

I tried to then double escape each .

using the code username.matches('^(?!\\.)(?!_)(?!.*\\.$)(?!.*?\\.\\.)[a-z0-9_.]+$')

It only shows one error (red ^ sign at the beginning), but then it gives me the error below

Invalid regular expression pattern. Pattern: ^(?!\.)(?!_)(?!.*\.$)(?!.*?\.\.)[a-z0-9_.]+$.

Can anyone let me know what I'm doing wrong?

解决方案

RE2 does not support lookaheads (nor lookbehinds).

However, the pattern can be re-written without lookarounds:

^[a-z0-9][a-z0-9_]*([.][a-z0-9_]+)*$

Details

• ^ - start of string
• [a-z0-9] - a letter or digit
• [a-z0-9_]* - zero or more lowercase letters, digits, or underscores
• ([.][a-z0-9_]+)* - zero or more sequences of
  • [.] - a dot
  • [a-z0-9_]+ - one or more lowercase letters, digits, or underscores
• $ - end of string.

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