Perl正则表达式重复匹配

Question

使用 '?' 时我遇到了奇怪的行为 正则表达式重复。我正在处理日志文件，在其中搜索特定的 HTTP 错误响应，例如。401. 该行可能包含但可能不包含响应正文。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。我希望它应该与.*?$match.*?线条的最小部分相匹配并为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. 正则表达式有什么问题？我怀疑.*?前面的非贪婪模式(?:body...)?吃掉输入，因为它可以与可选主体一起使用。

如何编写正确的正则表达式？

Answer 1

使用您显示的样本，您能否尝试以下操作。

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

这是上述正则表达式的在线演示

说明：为以上添加详细说明。

^                                          ##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.

Answer 2

您可以使用组 4 的可选部分并断言字符串的结尾。

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

• ^ 字符串的开始
• (.*?)\s+\|捕获组 1尽可能匹配任何字符并匹配空格和|
• \s+(\w+)\s+\|匹配空格并捕获第 2 组中的1+ 个单词字符并匹配空格和|
• \s+\[([^][]*)\]匹配空格和捕获所有之间[...]的第3组
• .*? 尽可能匹配任何字符
• (?:\s+\|\s+body:\h+({.*}))?可选地|在空格之间匹配，body:并{...}在组 4 中捕获所有之间
• $ 字符串结束

正则表达式演示

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，你仍然可以得到 的值$tstamp，$level并且$thread