Perl 正则表达式重复匹配

Question

我在使用“?”时遇到了奇怪的行为正则表达式重复。我正在处理日志文件，我正在其中搜索特定的 HTTP 错误响应，例如。 401. 该行可以但不可以包含响应正文。所以我想匹配这两种情况。我有以下代码。

#!/usr/bin/perl
$match = 'response 401';
$line = '2021-04-08 07:15:01 |  INFO | [http-nio-8080-exec-11] | rId:123456789 | ip:127.0.0.1 | activationId: abcdefg | user: admin | response 401: headers: Cache-Control: [no-cache, no-store, max-age=0, must-revalidate] / Content-Length: [60] / Content-Type: [application/json;charset=UTF-8] / Date: [Thu, 08 Apr 2021 05:15:01 GMT] / Expires: [0] / Pragma: [no-cache] | body: {"errors":[{"message":"Bad credentials","repeatable":true}]}';
    
my($tstamp, $level, $thread, $body) = $line =~ m/^(.*?)\s+\|\s+(\w+)\s+\|\s+\[(.*?)\].*?$match.*?(?:body\:\s+({.*}))?/;
if($body) {
  print "body: $body\n";
}

这不会打印任何内容。我希望它应该作为 .*?$match.*? 应该匹配行的最小部分并为 body 模式留出足够的空间。但显然不会。当我更改正则表达式并从 body 模式中删除 ? 并使其成为强制行匹配时。

my($tstamp, $level, $thread, $body) = $line =~ m/^(.*?)\s+\|\s+(\w+)\s+\|\s+\[(.*?)\].*?$match.*?(?:body\:\s+({.*}))/;

但这不会匹配没有 body 的行。正则表达式有什么问题？我怀疑 (?:body...)? 模式之前的非贪婪 .*? 模式吃掉了输入，因为可选主体没问题。

如何写出正确的正则表达式？

Answer 1

您可以使用第 4 组的可选部分并断言字符串的结尾。

^(.*?)\s+\|\s+(\w+)\s+\|\s+\[([^][]*)\].*?(?:\s+\|\s+body:\s+({.*}))?$

^ 字符串开头
(.*?)\s+\| 捕获 组 1 尽可能匹配任何字符并匹配空格和 |
\s+(\w+)\s+\| 匹配空格并捕获 组 2 中的 1+ 个单词字符并匹配空格和 |
\s+\[([^][]*)\] 匹配空格并捕获 第 3 组

[...]

.*? 尽可能少地匹配任何字符
(?:\s+\|\s+body:\h+({.*}))? 可选择在空格之间匹配 |，body: 并捕获 组 4[=52 中 {...} 之间的所有内容=]
$ 字符串结束

Regex demo

使用示例代码：

$match = 'response 401';
$line = '2021-04-08 07:15:01 |  INFO | [http-nio-8080-exec-11] | rId:123456789 | ip:127.0.0.1 | activationId: abcdefg | user: admin | response 401: headers: Cache-Control: [no-cache, no-store, max-age=0, must-revalidate] / Content-Length: [60] / Content-Type: [application/json;charset=UTF-8] / Date: [Thu, 08 Apr 2021 05:15:01 GMT] / Expires: [0] / Pragma: [no-cache] | body: {"errors":[{"message":"Bad credentials","repeatable":true}]}';

my($tstamp, $level, $thread, $body) = $line =~ m/^(.*?)\s+\|\s+(\w+)\s+\|\s+\[([^][]*)\].*?(?:\s+\|\s+body:\s+({.*}))?$/;
if($body) {
  print "body: $body\n";
}

输出

body: {"errors":[{"message":"Bad credentials","repeatable":true}]}

如果没有body，仍然可以获得$tstamp、$level和$thread

的值

Answer 2

根据您展示的示例，请您尝试以下操作。

^(\d{4}-\d{2}-\d{2}\s*(?:\d{2}:){2}\d{2})\s+\|\s+(\S+)\s+\|\s+\[([^]]*)\].*?(body.*)?$

Here is online demo for above regex

解释： 为以上添加详细解释。

^                                          ##Matching starting of value by caret sign.
(\d{4}-\d{2}-\d{2}\s*(?:\d{2}:){2}\d{2})   ##Creating 1st capturing group to match time stamp here.
\s+\|\s+                                   ##Matching spaces pipe spaces(one or more occurrences).
(\S+)                                      ##Creating 2nd capturing group which has everything apart from space, which will have INFO/WARN/ERROR etc here.
\s+\|\s+\[                                 ##Matching spaces pipe spaces(one or more occurrences).
([^]]*)                                    ##Creating 3rd capturing group which has everything till ] occurrence in it.
\].*?                                      ##Matching ] with lazy match.
(body.*)?$                                 ##Creating 4th capturing group which will match from body to till end of line and keeping it optional at the end of the line/value.

Perl 正则表达式重复匹配

Perl regex repetition match

regex

perl