javascript Javascript正则表达式匹配完全限定域名，无协议，可选子域
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Javascript regex to match fully qualified domain name, without protocol, optional subdomain
提问by Jared Eitnier
I haven't been able to find this one and what I'm trying isn't quite working out for me.
我一直无法找到这个，而且我正在尝试的方法对我来说并不完全有效。
I want to match only domains that:
我只想匹配以下域：
- don't contain a protocol (http, https, ftp)
- optionally include a subdomain
- don't startwith a hyphen but cancontain a hyphen
- 不包含协议（http、https、ftp）
- 可选地包括一个子域
- 不要以连字符开头，但可以包含连字符
Example domains that would match:
匹配的示例域：
- domain.com
- example.domain.com
- example.domain-hyphen.com
- www.domain.com
- example.museum
- 域名.com
- example.domain.com
- example.domain-hyphen.com
- www.domain.com
- 例子.博物馆
Example domains that would notmatch:
不匹配的示例域：
- http://example.com
- subdomain.-example.com
- example.com/parameter
- example.com?anything
- www.subdomain.domain.com
- http://example.com
- 子域.-example.com
- 例子.com/参数
- example.com？任何东西
- www.subdomain.domain.com
What I've currently got:
我目前所拥有的：
/^(?!:\/\/)(^[a-zA-Z0-9])?.[a-zA-Z0-9-]+\.[a-zA-Z]{2,6}?$/i
It's not matching protocols, allowing hyphen inside the domain, not allowing trailing characters after the TLD, and is allowing a subdomain (but only 1 character).
它不匹配协议，允许在域内使用连字符，不允许在 TLD 后使用尾随字符，并且允许使用子域（但只有 1 个字符）。
I still need to allow subdomains of any length, not allow www.subdomain.domain.com and not allow a leading hyphen.
我仍然需要允许任何长度的子域，不允许 www.subdomain.domain.com 并且不允许前导连字符。
回答by dda
Try
尝试
/^(?!:\/\/)([a-zA-Z0-9]+\.)?[a-zA-Z0-9][a-zA-Z0-9-]+\.[a-zA-Z]{2,6}?$/i
回答by Bergi
Let's analyse your regex:
让我们分析您的正则表达式：
^(?!:\/\/)
^(?!:\/\/)
This is pretty useless. While it indicates the intention of the regex, it's unnecessary since the following characters are not allowed to contain slashes anyway.
这很没用。虽然它表明了正则表达式的意图，但它是不必要的，因为无论如何都不允许以下字符包含斜杠。
(^[a-zA-Z0-9])?.
(^[a-zA-Z0-9])?.
I think you wanted this to be ^([a-zA-Z0-9]+\.)?. Your dot is not escaped, and would be preceded by only one optional character at the string beginning.
我想你想要这个^([a-zA-Z0-9]+\.)?。您的点不会被转义，并且在字符串开头只会有一个可选字符。
[a-zA-Z0-9-]+
[a-zA-Z0-9-]+
If you want this not to begin with a hyphen, you either could use a negative lookahead or better just [a-zA-Z0-9][a-zA-Z0-9-]*.
如果您不希望它以连字符开头，您可以使用否定前瞻或更好的[a-zA-Z0-9][a-zA-Z0-9-]*.
\.[a-zA-Z]{2,6}?
\.[a-zA-Z]{2,6}?
Not sure what the question mark does here. There's no backtracking anyway?
不知道问号在这里做什么。反正没有回溯？
/i
/i
This renders the explicit [a-zA-Z]useless, one would be enough. Or omit the iflag.
这使得显式[a-zA-Z]无用，一个就足够了。或者省略i标志。
All these things together, we will end up with
所有这些事情在一起，我们将结束
/^([a-z0-9]+\.)?[a-z0-9][a-z0-9-]*\.[a-z]{2,6}$/i
回答by Dharmesh Hadiyal
回答by Michal Aron
The RegEx I came up with while doing the Hostname/FQDN validation in Javascript:
我在 Javascript 中进行主机名/FQDN 验证时想到的正则表达式：
FQDN:
域名：
^(?!:\/\/)(?!.{256,})(([a-z0-9][a-z0-9_-]*?\.)+?[a-z]{2,6}?)$/i
^(?!:\/\/)(?!.{256,})(([a-z0-9][a-z0-9_-]*?\.)+?[a-z]{2,6}?)$/i
Hostname or FQDN
主机名或 FQDN
^(?!:\/\/)(?!.{256,})(([a-z0-9][a-z0-9_-]*?)|([a-z0-9][a-z0-9_-]*?\.)+?[a-z]{2,6}?)$/i
^(?!:\/\/)(?!.{256,})(([a-z0-9][a-z0-9_-]*?)|([a-z0-9][a-z0-9_-]*?\.)+?[a-z]{2,6}?)$/i
Both expressions use lookahead to check the total string length, which can be up to 255 characters. They also do a lazy check .{x,y}?.
这两个表达式都使用前瞻来检查总字符串长度，最多可以包含 255 个字符。他们还做一个懒惰的检查.{x,y}?。
Note that it is using case insensitive match /i.
请注意，它使用不区分大小写的 match /i。
