[系统运维]14、nginx的正则表达式名称-(server_name为正则表达式)

官网：Server names

翻译部分：?Regular expressions names

开始！

The regular expressions used by nginx are compatible with those used by the Perl programming language (PCRE).

?nginx用的正则表达式和那些被PCRE用的正则表达式是可共用的。

To use a regular expression, the server name must start with the tilde character:

?为了用正则表达式，server_name的参数必须以~开头。

server_name  ~^www\d+\.example\.net$;

?可以看到,~和参数之间不需要加空格。

otherwise it will be treated as an exact name, or if the expression contains an asterisk, as a wildcard name (and most likely as an invalid one).

?否则它将会被视为确切的名称，或者如果表达式包含星号，它会被视为通配符名称。

Do not forget to set “^” and “$” anchors.

??不要忘记设置^和$锚点。

They are not required syntactically, but logically.

?它们不是语法上需要的，而是语法上需要的。

Also note that domain name dots should be escaped with a backslash.

?同时也要记得域名点要用反斜杠转义 ,例如： \.

A regular expression containing the characters “{” and “}” should be quoted:

?包含{和}的正则表达式应该被""包围，如下：

server_name  "~^(?<name>\w\d{1,3}+)\.example\.net$";

otherwise nginx will fail to start and display the error message:

否则，nginx会启动失败并展示错误信息，错误信息如下：?

directive "server_name" is not terminated by ";" in ...

A named regular expression capture can be used later as a variable:

?在正则表达式中?<>包围的名字(如下的domain)可以稍后在后面作为一个变量来使用。

server {
    server_name   ~^(www\.)?(?<domain>.+)$;

    location / {
        root   /sites/$domain;
    }
}

The PCRE library supports named captures using the following syntax:

PCRE库支持使用以下语法的命名捕获：?

?<name>	Perl 5.10 compatible syntax, supported since PCRE-7.0 Perl5.10兼容语法，从PCRE-7.0开始支持。
?'name'	Perl 5.10 compatible syntax, supported since PCRE-7.0 Perl5.10兼容语法，从PCRE-7.0开始支持。
?P<name>	Python compatible syntax, supported since PCRE-4.0 Python兼容语法，从PCRE-4.0开始支持。

If nginx fails to start and displays the error message:

如果nginx启动失败并展示一下错误信息：?

pcre_compile() failed: unrecognized character after (?< in ...?

this means that the PCRE library is old and the syntax “?P<name>” should be tried instead.

这意味着PCRE库是旧版的，应该用?P<name>试试。?

The captures can also be used in digital form:

?捕获也可以用数字形式使用：

server {
    server_name   ~^(www\.)?(.+)$;

    location / {
        root   /sites/$2;
    }
}

$2表示正则表达式匹配到的第2个参数?，

如果匹配到www.example.com,那$2就是example.com。

~^(www\.)?(.+)$解释：

1.~表示这是一个正则表达式

2.^表示以后面匹配的内容开头

3.(www\.)表示匹配www.，结合^就是匹配以www.开头的字符串

4.?表示前面的子表达式匹配最多1次，结合上面是：只能匹配www.0次或1次

5.(.+)表示匹配单个字符至少1次，.表示匹配除换行符 \n 之外的任何单字符,+表示匹配1次或多次

6.$表示以前面匹配的字符串结尾?

However, such usage should be limited to simple cases (like the above), since the digital references can easily be overwritten.

然而，这种用法应该只限于简单的情况，因为数字引用很容易被覆盖。