Ruby 仅捕获网站的一部分_Ruby_Regex

Ruby 仅捕获网站的一部分

ruby regex

Ruby 仅捕获网站的一部分,ruby,regex,Ruby,Regex,我有一个这样的正则表达式 /（？：http[s]？：\/\/）（？：www\）？（.*）/ 我只想捕获任何网站的域部分，而不考虑协议。因此，这个正则表达式可以工作，但它也捕获一些空白。这里的空白是从哪里来的？如果我明白这一点，它可能会对我很有帮助如果我输入以下字符串进行匹配投入： http://google.com https://www.simplecms.com www.facebook.com gmail.com 产出： Match 1 1. google.com Match 2

我有一个这样的正则表达式

/（？：http[s]？：\/\/）（？：www\）？（.*）/

我只想捕获任何网站的域部分，而不考虑协议。因此，这个正则表达式可以工作，但它也捕获一些空白。这里的空白是从哪里来的？如果我明白这一点，它可能会对我很有帮助

如果我输入以下字符串进行匹配

投入：

http://google.com
https://www.simplecms.com
www.facebook.com
gmail.com

产出：

Match 1
1.  google.com
Match 2
1.   
Match 3
1.  simplecms.com
Match 4
1.   
Match 5
1.  facebook.com
Match 6
1.   
Match 7
1.  gmail.com
Match 8
1.   
Match 9
1.

如果查看输出，它完成了任务，但也捕获了一些空字符串。我相信有更好的方法来捕捉这一点。

我可以采用这种非正则表达式的方法：-

require 'uri'

str = <<-eot
http://google.com
https://www.simplecms.com
www.facebook.com
gmail.com
eot

str.split.map{|u| uri=URI(u); uri.scheme ? uri.host : u}
# => ["google.com", "www.simplecms.com", "www.facebook.com", "gmail.com"]

require'uri'
str=尝试将行的开始/结束添加到正则表达式的开始和结束<代码>^

在开始处

在结束处，与行匹配。我认为现在发生的是你的正则表达式看到了回报并与之匹配

请尝试：

^（？：http[s]？：\/\/）（？：www\.）？（.*）$

（注意：根据语言的不同，您可能需要转义）

使用您提供的示例，我设置了一个。

不要尝试重新创建用于解析URL的模式

下面是一个使用Ruby类的模式的快速列表。您不需要直接访问它们，因为有些方法提供了所需的逻辑来处理模式无法处理的情况

实际定义在URI中：

哪些产出：

:ALPHA => %r/a-zA-Z/x
:ALNUM => %r/a-zA-Z\d/x
:HEX => %r/a-fA-F\d/x
:ESCAPED => %r/%[a-fA-F\d]{2}/x
:UNRESERVED => %r/\-_.!~*'()a-zA-Z\d/x
:RESERVED => %r/;/?:@&=+$,\[\]/x
:DOMLABEL => %r/(?:[a-zA-Z\d](?:[-a-zA-Z\d]*[a-zA-Z\d])?)/x
:TOPLABEL => %r/(?:[a-zA-Z](?:[-a-zA-Z\d]*[a-zA-Z\d])?)/x
:HOSTNAME => %r/(?:(?:[a-zA-Z\d](?:[-a-zA-Z\d]*[a-zA-Z\d])?)\.)*(?:[a-zA-Z](?:[-a-zA-Z\d]*[a-zA-Z\d])?)\.?/x
:URIC => %r/(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})/x
:URIC_NO_SLASH => %r/(?:[\-_.!~*'()a-zA-Z\d;?:@&=+$,]|%[a-fA-F\d]{2})/x
:QUERY => %r/(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*/x
:FRAGMENT => %r/(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*/x
:IPV4ADDR => %r/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/x
:IPV6ADDR => %r/(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)/x
:IPV6REF => %r/\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\]/x
:HOST => %r/(?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\])/x
:HOSTPORT => %r/(?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\])(?::\d*)?/x
:USERINFO => %r/(?:[\-_.!~*'()a-zA-Z\d;:&=+$,]|%[a-fA-F\d]{2})*/x
:PATH_SEGMENTS => %r/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*/x
:REG_NAME => %r/(?:[\-_.!~*'()a-zA-Z\d$,;:@&=+]|%[a-fA-F\d]{2})+/x
:REL_SEGMENT => %r/(?:[\-_.!~*'()a-zA-Z\d;@&=+$,]|%[a-fA-F\d]{2})+/x
:SCHEME => %r/[a-zA-Z][\-+.a-zA-Z\d]*/x
:ABS_PATH => %r//(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*/x
:REL_PATH => %r/(?:[\-_.!~*'()a-zA-Z\d;@&=+$,]|%[a-fA-F\d]{2})+(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?/x
:NET_PATH => %r///(?:(?:(?:[\-_.!~*'()a-zA-Z\d;:&=+$,]|%[a-fA-F\d]{2})*@)?(?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\])(?::\d*)?|(?:[\-_.!~*'()a-zA-Z\d$,;:@&=+]|%[a-fA-F\d]{2})+)(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?/x
:HIER_PART => %r/(?://(?:(?:(?:[\-_.!~*'()a-zA-Z\d;:&=+$,]|%[a-fA-F\d]{2})*@)?(?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\])(?::\d*)?|(?:[\-_.!~*'()a-zA-Z\d$,;:@&=+]|%[a-fA-F\d]{2})+)(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?|/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)(?:\?(?:(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*))?/x
:OPAQUE_PART => %r/(?:[\-_.!~*'()a-zA-Z\d;?:@&=+$,]|%[a-fA-F\d]{2})(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*/x
:ABS_URI => %r/[a-zA-Z][\-+.a-zA-Z\d]*:(?:(?://(?:(?:(?:[\-_.!~*'()a-zA-Z\d;:&=+$,]|%[a-fA-F\d]{2})*@)?(?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\])(?::\d*)?|(?:[\-_.!~*'()a-zA-Z\d$,;:@&=+]|%[a-fA-F\d]{2})+)(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?|/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)(?:\?(?:(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*))?|(?:[\-_.!~*'()a-zA-Z\d;?:@&=+$,]|%[a-fA-F\d]{2})(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*)/x
:REL_URI => %r/(?://(?:(?:(?:[\-_.!~*'()a-zA-Z\d;:&=+$,]|%[a-fA-F\d]{2})*@)?(?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\])(?::\d*)?|(?:[\-_.!~*'()a-zA-Z\d$,;:@&=+]|%[a-fA-F\d]{2})+)(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?|/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*|(?:[\-_.!~*'()a-zA-Z\d;@&=+$,]|%[a-fA-F\d]{2})+(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?)(?:\?(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*)?/x
:URI_REF => %r/(?:[a-zA-Z][\-+.a-zA-Z\d]*:(?:(?://(?:(?:(?:[\-_.!~*'()a-zA-Z\d;:&=+$,]|%[a-fA-F\d]{2})*@)?(?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\])(?::\d*)?|(?:[\-_.!~*'()a-zA-Z\d$,;:@&=+]|%[a-fA-F\d]{2})+)(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?|/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)(?:\?(?:(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*))?|(?:[\-_.!~*'()a-zA-Z\d;?:@&=+$,]|%[a-fA-F\d]{2})(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*)|(?://(?:(?:(?:[\-_.!~*'()a-zA-Z\d;:&=+$,]|%[a-fA-F\d]{2})*@)?(?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\])(?::\d*)?|(?:[\-_.!~*'()a-zA-Z\d$,;:@&=+]|%[a-fA-F\d]{2})+)(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?|/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*|(?:[\-_.!~*'()a-zA-Z\d;@&=+$,]|%[a-fA-F\d]{2})+(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?)(?:\?(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*)?)?(?:#(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*)?/x
:X_ABS_URI => %r/
        ([a-zA-Z][\-+.a-zA-Z\d]*):                           (?# 1: scheme)
        (?:
           ((?:[\-_.!~*'()a-zA-Z\d;?:@&=+$,]|%[a-fA-F\d]{2})(?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*)                    (?# 2: opaque)
        |
           (?:(?:
             //(?:
                 (?:(?:((?:[\-_.!~*'()a-zA-Z\d;:&=+$,]|%[a-fA-F\d]{2})*)@)?        (?# 3: userinfo)
                   (?:((?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\]))(?::(\d*))?))? (?# 4: host, 5: port)
               |
                 ((?:[\-_.!~*'()a-zA-Z\d$,;:@&=+]|%[a-fA-F\d]{2})+)                 (?# 6: registry)
               )
             |
             (?!//))                           (?# XXX: '//' is the mark for hostport)
             (/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?                    (?# 7: path)
           )(?:\?((?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*))?                 (?# 8: query)
        )
        (?:\#((?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*))?                  (?# 9: fragment)
      /x
:X_REL_URI => %r/
        (?:
          (?:
            //
            (?:
              (?:((?:[\-_.!~*'()a-zA-Z\d;:&=+$,]|%[a-fA-F\d]{2})*)@)?       (?# 1: userinfo)
                ((?:(?:[a-zA-Z0-9\-.]|%\h\h)+|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|\[(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|(?:(?:[a-fA-F\d]{1,4}:)*[a-fA-F\d]{1,4})?::(?:(?:[a-fA-F\d]{1,4}:)*(?:[a-fA-F\d]{1,4}|\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}))?)\]))?(?::(\d*))?  (?# 2: host, 3: port)
            |
              ((?:[\-_.!~*'()a-zA-Z\d$,;:@&=+]|%[a-fA-F\d]{2})+)             (?# 4: registry)
            )
          )
        |
          ((?:[\-_.!~*'()a-zA-Z\d;@&=+$,]|%[a-fA-F\d]{2})+)              (?# 5: rel_segment)
        )?
        (/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*(?:/(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*(?:;(?:[\-_.!~*'()a-zA-Z\d:@&=+$,]|%[a-fA-F\d]{2})*)*)*)?                  (?# 6: abs_path)
        (?:\?((?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*))?              (?# 7: query)
        (?:\#((?:[\-_.!~*'()a-zA-Z\d;/?:@&=+$,\[\]]|%[a-fA-F\d]{2})*))?           (?# 8: fragment)
      /x

URI希望字符串以某种模式开头。当您知道主机是一个网站时，您可以通过在“http://”前面加上前缀来愚弄它，或者直接按原样使用主机。如果传入的字符串不止是主机，请在“http://”之前加上前缀，并让URI剥离字符串的各个部分：

require 'uri'

hosts = %w[
  http://google.com
  https://www.simplecms.com
  www.facebook.com
  gmail.com
  http://foo.com/posts?id=30&limit=5#time=1305298413
  https://foo.com/posts?id=30&limit=5#time=1305298413
  foo.com/posts?id=30&limit=5#time=1305298413
  ].map { |url|

    scheme, userinfo, host, port, registry, path, opaque, query, fragment = case !!url[%r(\Ahttps?://)i]
    when true
      URI.split(url)
    when false
      URI.split("http://#{ url }")
    end

    host
  }
hosts # => ["google.com", "www.simplecms.com", "www.facebook.com", "gmail.com", "foo.com", "foo.com", "foo.com"]

您还可以直接访问主机组件：

url = "http://foo.com/posts?id=30&limit=5#time=1305298413"
uri = URI(url)
uri.host # => "foo.com"

scheme, userinfo, host, port, registry, path, opaque, query, fragment = URI.split("http://#{ url }") 
scheme # => "http"
userinfo # => nil
host # => "http"
port # => ""
registry # => nil
path # => "//foo.com/posts"
opaque # => nil
query # => "id=30&limit=5"
fragment # => "time=1305298413"

上面关于URI希望看到方案的警告仍然适用

URI是“FTW”，因为它可以分解字符串，并允许您访问每个组件。它还允许您以符合RFC的方式构建或修改URI

如果URI不够复杂，那么还有一种更为FTW的方法。

一种更简单的方法可以用于您的用例：

> sites
 => ["http://google.com", "https://www.simplecms.com", "www.facebook.com", "gmail.com"] 
> sites.map{|s| s.split('/').last}
 => ["google.com", "www.simplecms.com", "www.facebook.com", "gmail.com"]

不要使用正则表达式，只需使用内置表达式：

为什么要使用正则表达式？什么意思？我想学习，或者我有一些任务需要捕获字符串的一部分。你有什么更好的建议吗？欢迎你。感谢现在，任何一种刚刚起步并与网络有过客关系的语言，都应该有预先构建的工具来处理互联网和URI。重复使用这些，不要试图重新发明轮子。花一个小时进行研究可以为您节省数日的编写和调试时间。如果你在研究之后找不到任何合适的方法，那么就用经过良好测试的正则表达式模式写一些东西。这些模式有多个可用的来源，因此，同样地，您不必重新创建甚至修改它们。有关更多信息，请参阅。这正是发生的情况。非常感谢。

> sites
 => ["http://google.com", "https://www.simplecms.com", "www.facebook.com", "gmail.com"] 
> sites.map{|s| s.split('/').last}
 => ["google.com", "www.simplecms.com", "www.facebook.com", "gmail.com"]

require 'uri'

def get_domain(url)
  url = 'http://' + url unless url =~ /^https?:\/\//i
  begin
    URI.parse(url).host
  rescue URI::InvalidURIError
    nil
  end
end

get_domain('http://google.com')         # => google.com
get_domain('https://www.simplecms.com') # => www.simplecms.com
get_domain('www.facebook.com')          # => www.facebook.com
get_domain('gmail.com')                 # => gmail.com