Javascript 匹配模式或为空字符串的正则表达式

Regular expression which matches a pattern, or is an empty string

提问by Curt

I have the following Regular Expression which matches an email address format:

我有以下与电子邮件地址格式匹配的正则表达式：

^[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+$

This is used for validation with a form using JavaScript. However, this is an optional field. Therefore how can I change this regex to match an email address format, or an empty string?

这用于验证使用 JavaScript 的表单。但是，这是一个可选字段。因此，如何更改此正则表达式以匹配电子邮件地址格式或空字符串？

From my limited regex knowledge, I think \bmatches an empty string, and |means "Or", so I tried to do the following, but it didn't work:

根据我有限的正则表达式知识，我认为\b匹配一个空字符串，|表示“或”，所以我尝试执行以下操作，但没有奏效：

^[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+$|\b

回答by polygenelubricants

To match patternor an empty string, use

要匹配pattern或空字符串，请使用

^$|pattern

Explanation

解释

• ^and $are the beginning and end of the string anchors respectively.
• |is used to denote alternates, e.g. this|that.

• ^和$分别是字符串锚点的开始和结束。
• |用于表示替代，例如this|that。

References

参考

• regular-expressions.info/Anchorsand Alternation

• 正则表达式.info/Anchorsand Alternation

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On \b

在 \b

\bin most flavor is a "word boundary" anchor. It is a zero-width match, i.e. an empty string, but it only matches those strings at very specific places, namely at the boundaries of a word.

\b在大多数风味中是一个“词边界”锚。它是一个零宽度匹配，即一个空字符串，但它只在非常特定的地方匹配那些字符串，即在单词的边界处。

That is, \bis located:

也就是说，\b位于：

• Between consecutive \wand \W(either order):
  • i.e. between a word character and a non-word character
• Between ^and \w
  • i.e. at the beginning of the string if it starts with \w
• Between \wand $
  • i.e. at the end of the string if it ends with \w

• 在连续\w和\W（任一顺序）之间：
  • 即在单词字符和非单词字符之间
• ^和之间\w
  • 即在字符串的开头，如果它以 \w
• \w和之间$
  • 即在字符串的末尾，如果它以 \w

References

参考

• regular-expressions.info/Word Boundaries

• 正则表达式.info/Word Boundaries

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On using regex to match e-mail addresses

使用正则表达式匹配电子邮件地址

This is not trivial depending on specification.

根据规范，这不是微不足道的。

Related questions

相关问题

• What is the best regular expression for validating email addresses?
• Regexp recognition of email address hard?
• How far should one take e-mail address validation?

• 验证电子邮件地址的最佳正则表达式是什么？
• 正则表达式识别电子邮件地址很难吗？
• 电子邮件地址验证应该走多远？

回答by Jgonzalez731

An alternative would be to place your regexp in non-capturing parentheses. Then make that expression optional using the ?qualifier, which will look for 0 (i.e. empty string) or 1 instances of the non-captured group.

另一种方法是将您的正则表达式放在非捕获括号中。然后使用?限定符将该表达式设为可选，它将查找未捕获组的 0（即空字符串）或 1 个实例。

For example:

例如：

/(?: some regexp )?/

In your case the regular expression would look something like this:

在您的情况下，正则表达式将如下所示：

/^(?:[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+)?$/

No |"or" operator necessary!

不需要|“或”运算符！

Hereis the Mozilla documentation for JavaScript Regular Expression syntax.

这是 JavaScript 正则表达式语法的 Mozilla 文档。

回答by Zano

I'm not sure why you'd want to validate an optional email address, but I'd suggest you use

我不确定您为什么要验证可选的电子邮件地址，但我建议您使用

^$|^[^@\s]+@[^@\s]+$

meaning

意义

^$        empty string
|         or
^         beginning of string
[^@\s]+   any character but @ or whitespace
@         
[^@\s]+
$         end of string

You won't stop fake emails anyway, and this way you won't stop valid addresses.

无论如何，您都不会阻止虚假电子邮件，这样您就不会阻止有效地址。

回答by pritaeas

\b matches a word boundary. I think you can use ^$ for empty string.

\b 匹配单词边界。我认为您可以将 ^$ 用于空字符串。