正则表达式 密码数字字母特殊字符
    ## English Answer.
    Regular expressions are a powerful tool for matching patterns in text. They can be used to validate input, find and replace text, and perform a variety of other tasks.
    When it comes to passwords, there are a few common requirements that you may want to enforce. These requirements typically include:
    Minimum length: The password must be at least a certain number of characters long.
    Maximum length: The password cannot be longer than a certain number of characters.
    Character types: The password must contain at least one character from each of the following character types:
        Uppercase letters.
        Lowercase letters.
        Numbers.
        Special characters.
    The following regular expression will match passwords that meet all of these requirements:
    ^(?=.[a-z])(?=.[A-Z])(?=.\d)(?=.[@$!%?&])[A-Za-z\d@$!%?&]{8,}$。
    This regular expression can be broken down into the following parts:
    `^`: This anchor matches the beginning of the string.
    `(?=.[a-z])`: This positive lookahead assertion matches if the password contains at least one lowercase letter.
    `(?=.[A-Z])`: This positive lookahead assertion matches if the password contains at least one uppercase letter.
    `(?=.\d)`: This positive lookahead assertion matches if the password contains at least one digit.
    `(?=.[@$!%?&])`: This positive lookahead assertion matches if the password contains at least one special character.
    `[A-Za-z\d@$!%?&]{8,}$`: This character class matches any character from the following character set: uppercase letters, lowercase letters, digits, and special characters. The `{8,}` quantifier matches if the password is at least 8 characters long. The `$` anchor matches the end of the string.
    ## 中文回答。
密码字符串是什么
    正则表达式是一种用于匹配文本中模式的强大工具。它们可以用于验证输入，查和替换文本，以及执行各种其他任务。
    在密码方面，您可能需要强制执行一些常见要求。这些要求通常包括：
    最小长度，密码必须至少包含一定数量的字符。
    最大长度，密码不能超过一定数量的字符。
    字符类型：密码必须至少包含以下每种字符类型的字符之一：
        大写字母。
        小写字母。
        数字。
        特殊字符。
    以下正则表达式将匹配满足所有这些要求的密码：
    ^(?=.[a-z])(?=.[A-Z])(?=.\d)(?=.[@$!%?&])[A-Za-z\d@$!%?&]{8,}$。
    这个正则表达式可以分解为以下部分：
    `^`，此锚点匹配字符串的开头。
    `(?=.[a-z])`，此肯定前瞻断言匹配密码是否包含至少一个小写字母。
    `(?=.[A-Z])`，此肯定前瞻断言匹配密码是否包含至少一个大写字母。
    `(?=.\d)`，此肯定前瞻断言匹配密码是否包含至少一个数字。
    `(?=.[@$!%?&])`，此肯定前瞻断言匹配密码是否包含至少一个特殊字符。
    `[A-Za-z\d@$!%?&]{8,}$`，此字符类匹配以下字符集中的任何字符，大写字母、小写字母、数字和特殊字符。`{8,}` 量词匹配密码至少为 8 个字符。`$` 锚点匹配字符串的末尾。

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