regex - Perl RegEx 非捕获组在组内具有替代捕获

Question

我正在尝试解析一些邮件日志，这些日志具有以下三种可能的中继格式。

Oct 24 03:49:10 mxout/mxout/1.1.1.1 sendmail[4642]: x9NA4Wbp011336: to=<email@company.com>, delay=1+00:44:37, xdelay=00:00:00, mailer=esmtp, pri=459, relay=mail-company.com. [0.0.0.0], tls=no, dsn=4.0.0, stat=Deferred: Connection reset by mail-company.com
Oct 24 03:49:10 mxout/mxout/1.1.1.1 sendmail[4642]: x9NA4Wbp011336: to=<email@company.com>, delay=1+00:44:37, xdelay=00:00:00, mailer=esmtp, pri=459, relay=[0.0.0.0], tls=no, dsn=4.0.0, stat=Deferred: Connection reset by mail-company.com
Oct 24 03:49:10 mxout/mxout/1.1.1.1 sendmail[4642]: x9NA4Wbp011336: to=<email@company.com>, delay=1+00:44:37, xdelay=00:00:00, mailer=esmtp, pri=459, relay=mail-company.com., tls=no, dsn=4.0.0, stat=Deferred: Connection reset by mail-company.com

使用此代码:

my $topat    = '^(\w{3})\s{1,2}(\d{1,2}) (\d{2}:\d{2}:\d{2}).+ sendmail\[\d.+\]: (\w+): to=<(\S+)>(?:,|, \[more\],) delay.+, relay=(?:(?:\S+ )?\[(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\]|(\S+)\.), .+, stat=(.+)';

foreach my $line(@i) {
  if($line =~ /$topat/){
    my ($month, $day, $time, $id, $addy, $relay, $stat) = ($line =~ m/$topat/);
     print $line;
     print "$addy $relay $stat\n";
  }
}

我收到以下错误:

Oct 24 03:49:10 mxout/mxout/1.1.1.1 sendmail[4642]: x9NA4Wbp011336: to=<email@company.com>, delay=1+00:44:37, xdelay=00:00:00, mailer=esmtp, pri=459, relay=mail-company.com. [0.0.0.0], tls=no, dsn=4.0.0, stat=Deferred: Connection reset by mail-company.com
Use of uninitialized value $stat in concatenation (.) or string at ./reg_test line 26.
email@company.com 0.0.0.0 

Oct 24 03:49:10 mxout/mxout/1.1.1.1 sendmail[4642]: x9NA4Wbp011336: to=<email@company.com>, delay=1+00:44:37, xdelay=00:00:00, mailer=esmtp, pri=459, relay=[0.0.0.0], tls=no, dsn=4.0.0, stat=Deferred: Connection reset by mail-company.com
Use of uninitialized value $stat in concatenation (.) or string at ./reg_test line 26.
email@company.com 0.0.0.0 

Oct 24 03:49:10 mxout/mxout/1.1.1.1 sendmail[4642]: x9NA4Wbp011336: to=<email@company.com>, delay=1+00:44:37, xdelay=00:00:00, mailer=esmtp, pri=459, relay=mail-company.com., tls=no, dsn=4.0.0, stat=Deferred: Connection reset by mail-company.com
Use of uninitialized value $relay in concatenation (.) or string at ./reg_test line 26.
email@company.com  mail-company.com

在前两种情况下，它正确地获取了地址和中继，但没有获取统计信息。在第三个中，它获取地址和中继，但它认为 $relay 是空白的，而 $stat 是中继。

我尝试了许多不同的配置和组，但似乎找不到正确的解决方案。任何指针将不胜感激。

Answer 1

您在 relay 中有两种选择 field :

relay=(?:(?:\S+ )?\[(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\]|(\S+)\.)
                    ^    ----      $6         ----     ^  | ^$7^ 

如果它不遵循第一个模式但与第二个模式匹配，则中继以 $7 结束。和 $stat . $stat永远不会正确填充，因为它需要 8 美元，而不是 7 美元。

您可以使用分支重置模式，该模式对所有备选方案使用相同的捕获编号:

(?|(?:\S+ )?\[(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\]|(\S+)\.)
  ^

或者，使用原始正则表达式并填充两个变量:

    my ($month, $day, $time, $id, $addy, $relay, $relay_alt, $stat) = $line =~ m/$topat/;
    $relay //= $relay_alt;