特别转义序列 ------------ PCRE 的转义符号例如 `\d`,`\s` 以及 `\w` 等需要特别注意，因为在字符串语义中，反斜线字符 `\` 会被 Lua 语言解析器和 Nginx 配置文件解析器在执行前同时处理掉，所以以下代码片段将无法按预期运行： ```nginx # nginx.conf ? location /test { ? content_by_lua ' ? local regex = "\d+" -- 这里是错的!! ? local m = ngx.re.match("hello, 1234", regex) ? if m then ngx.say(m[0]) else ngx.say("not matched!") end ? '; ? } # 结果为 "not matched!" ``` 为避免这个问题，需要双重转义反斜线符号： ```nginx # nginx.conf location /test { content_by_lua ' local regex = "\\\\d+" local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end '; } # 结果为 "1234" ``` 这里的 `\\\\d+`，先被 Nginx 配置文件解析器处理成 `\\d+` ，再被 Lua 语言解析器处理成 `\d+`，之后才被执行。 或者，正则表达式模板可以使用 Lua 字符串"长括号"语义写出，其语法形式为 `[[...]]`，在这种情况下，反斜线仅需为 Nginx 配置文件解析器转义一次。 ```nginx # nginx.conf location /test { content_by_lua ' local regex = [[\\d+]] local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end '; } # 结果为 to "1234" ``` 这里，`[[\\d+]]` 被 Nginx 配置文件解析器处理成 `[[\d+]]`，符合预期。 注意，当正则表达式模板中包括 `[...]` 序列时，Lua 语言中“更长的长括号”形式 `[=[...]=]` 是必要的。如果需要，可以将`[=[...]=]` 作为默认形式。 ```nginx # nginx.conf location /test { content_by_lua ' local regex = [=[[0-9]+]=] local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end '; } # 结果为 "1234" ``` 还有一种转义 PCRE 序列的方法是把 Lua 代码放到外部脚本文件中，通过各种 `*_by_lua_file` 指令执行。在这种方法中，反斜线仅被 Lua 语言解析器处理，因此只需要转义一次。 ```lua -- test.lua local regex = "\\d+" local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end -- 结果为 "1234" ``` 在外部脚本文件中，PCRE 序列如果使用“长括号”形式 Lua 字符串，则无需修改。 ```lua -- test.lua local regex = [[\d+]] local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end -- 结果为 "1234" ``` > English source: PCRE sequences such as `\d`, `\s`, or `\w`, require special attention because in string literals, the backslash character, `\`, is stripped out by both the Lua language parser and by the Nginx config file parser before processing. So the following snippet will not work as expected: ```nginx # nginx.conf ? location /test { ? content_by_lua ' ? local regex = "\d+" -- THIS IS WRONG!! ? local m = ngx.re.match("hello, 1234", regex) ? if m then ngx.say(m[0]) else ngx.say("not matched!") end ? '; ? } # evaluates to "not matched!" ``` To avoid this, *double* escape the backslash: ```nginx # nginx.conf location /test { content_by_lua ' local regex = "\\\\d+" local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end '; } # evaluates to "1234" ``` Here, `\\\\d+` is stripped down to `\\d+` by the Nginx config file parser and this is further stripped down to `\d+` by the Lua language parser before running. Alternatively, the regex pattern can be presented as a long-bracketed Lua string literal by encasing it in "long brackets", `[[...]]`, in which case backslashes have to only be escaped once for the Nginx config file parser. ```nginx # nginx.conf location /test { content_by_lua ' local regex = [[\\d+]] local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end '; } # evaluates to "1234" ``` Here, `[[\\d+]]` is stripped down to `[[\d+]]` by the Nginx config file parser and this is processed correctly. Note that a longer from of the long bracket, `[=[...]=]`, may be required if the regex pattern contains `[...]` sequences. The `[=[...]=]` form may be used as the default form if desired. ```nginx # nginx.conf location /test { content_by_lua ' local regex = [=[[0-9]+]=] local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end '; } # evaluates to "1234" ``` An alternative approach to escaping PCRE sequences is to ensure that Lua code is placed in external script files and executed using the various `*_by_lua_file` directives. With this approach, the backslashes are only stripped by the Lua language parser and therefore only need to be escaped once each. ```lua -- test.lua local regex = "\\d+" local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end -- evaluates to "1234" ``` Within external script files, PCRE sequences presented as long-bracketed Lua string literals do not require modification. ```lua -- test.lua local regex = [[\d+]] local m = ngx.re.match("hello, 1234", regex) if m then ngx.say(m[0]) else ngx.say("not matched!") end -- evaluates to "1234" ``` [返回目录](#nginx-api-for-lua)