正则表达式不能一次使用或不使用 [英] Regex expression not working with once or none

问题描述

下面是我的正则表达式:

Below is my regex:

[^4\d{3}-?\d{4}-?\d{4}-?\d{4}$]

但是它会在-处引发错误.我正在使用?，它应该允许-出现零次或一次.为什么会出现错误?

But it throws an error at -. I am using ?, which should allows - to appear zero or one time. Why it is giving errors?

推荐答案

正则表达式的问题在于，模式用[和]括起来，被视为字符类标记(请参见

The problem with the regex is that the pattern is enclosed with [ and ] that are treated as character class markers (see Character Classes or Character Sets):

使用字符类"(也称为字符集")，您可以告诉正则表达式引擎仅匹配几个字符中的一个.只需将要匹配的字符放在方括号之间.如果要匹配a或e，请使用[ae].

在字符类中，-在文字字符之间创建范围.在您的情况下，这些范围是无效的(从具有较高值的​​字符到具有较低值的字符)，因为{4}和其他子模式被视为单独的字符，而不是特殊的构造:

In character classes, - creates ranges between literal characters. In your case, these ranges are not valid (go from a character with higher values to those with lower values) since the {4} and other subpatterns were treated as separate characters, not special constructs:

因此，您要做的就是移除两侧的[和]:

So, all you need to do is remove the [ and ] on both sides:

^4\d{3}-?\d{4}-?\d{4}-?\d{4}$

请参见 regex演示.

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