正则表达式不允许双下划线 [英] Regex not to allow double underscores

问题描述

尝试应用正则表达式以不允许带有双下划线的字符串

Trying to apply regex for not allowing a string with double underscores

 [a-z][a-z0-9_-]+[^__]

但它在许多情况下都失败了，例如:

but its failing in many cases like:

ab_      doesn't matches whereas it should
ab__c_   matches whereas it shouldn't.

推荐答案

[^__] 匹配一个不是下划线的字符.要断言您的字符串没有两个连续的下划线，您可以使用 负前瞻:

[^__] matches one character that is not underscore. To assert that your string doesn't have two consecutive underscores, you could use a negative lookahead:

^(?!.*__.*)[a-z][a-z0-9_-]+$

环视断言您的字符串没有有两个连续的下划线(?!.*__.*)，然后如果断言没有匹配您所需的字符串失败 -- [az][a-z0-9_-]+.

The lookaround asserts that your string does not have two consecutive underscores (?!.*__.*), and then matches your required string if the assertion does not fail -- [a-z][a-z0-9_-]+.

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