正则表达式模式 - 什么是 ((?=.*\d)|(?=.*\W+)) 和 (?![.\n])

Question

有人可以向我解释这个正则表达式模式吗？

在下面

(?=^.{8,}$)((?=.*\d)|(?=.*\W+))(?![.\n])(?=.*[A-Z])(?=.*[a-z]).*$

究竟是什么

((?=.*\d)|(?=.*\W+))

&

(?![.\n])

谢谢你

Answer 1

这些都是先行断言(正面和负面)，以确保以下文本遵守某些规则，而无需实际捕获文本。

               # assert that
(?=^.{8,}$)    # there are at least 8 characters
(              # and
  (?=.*\d)       # there is at least a digit
  |              # or
  (?=.*\W+)      # there is one or more "non word" characters (\W is equivalent to [^a-zA-Z0-9_])
)              # and
(?![.\n])      # there is no . or newline and
(?=.*[A-Z])    # there is at least an upper case letter and
(?=.*[a-z]).*$ # there is at least a lower case letter
.*$            # in a string of any characters

(?! ... )是负前瞻的语法(如果没有...则匹配)， (?= ... )用于积极的前瞻(如果有......则匹配)。这看起来很像密码验证!