regex - Perl 可选捕获组不起作用？

Question

我有以下 sample.txt 文件:

2021-10-07 10:32:05,767 ERROR [LAWT2] blah.blah.blah - Message processing FAILED: <ExecutionReport blah="xxx" foo="yyy" SessionID="kkk" MoreStuff="zz"> Total time for which application threads were stopped: 0.0003858 seconds, Stopping threads took: 0.0000653 seconds
2021-10-07 10:31:32,902 ERROR [LAWT6] blah.blah.blah - Message processing FAILED: <NewOrderSingle SessionID="zkx" TargetSubID="ttt" Account="blah" MsgType="D" BookingTypeOverride="0" Symbol="6316" OtherField1="othervalue1" Otherfield2="othervalue2"/></D></NewOrderSingle>

我只想获取两个关键字段:“SessionID”和“MsgType”并像这样打印:

SessionID="kkk"|
SessionID="zkx"|MsgType="D"

换句话说:如果组匹配不存在，我只想打印空白。

我尝试了以下方法但没有成功:

$$ perl -ne '/ (SessionID=".*?")? .*(MsgType=".*?")? / and print "$1|$2\n"' sample.txt
SessionID="kkk"|
SessionID="zkx"|

有人能给我讲讲吗？非常感谢。

Answer 1

你可以使用

perl -ne '/\h(SessionID="[^"]*")?(?:\h++.*(MsgType="[^"]*"))?\h/ and print "$1|$2\n"' 

参见 regex demo . 详细信息:

• \h - 水平空格
• (SessionID="[^"]*")? - 第 1 组:可选的 SessionID="， 以外的任何零个或多个字符，然后是 "
• (?:\h++.*(MsgType=".*?"))? - 一个可选的(但贪婪的)序列
  • \h++ - 一个或多个水平空格
  • .* - 尽可能多的除换行符以外的任何零个或多个字符
  • (MsgType="[^"]*") - 第 2 组:SessionID="，" 以外的任何零个或多个字符>，然后是 "
• \h - 水平空格。

参见 online demo :

s='2021-10-07 10:32:05,767 ERROR [LAWT2] blah.blah.blah - Message processing FAILED: <ExecutionReport blah="xxx" foo="yyy" SessionID="kkk" MoreStuff="zz"> Total time for which application threads were stopped: 0.0003858 seconds, Stopping threads took: 0.0000653 seconds
2021-10-07 10:31:32,902 ERROR [LAWT6] blah.blah.blah - Message processing FAILED: <NewOrderSingle SessionID="zkx" TargetSubID="ttt" Account="blah" MsgType="D" BookingTypeOverride="0" Symbol="6316" OtherField1="othervalue1" Otherfield2="othervalue2"/></D></NewOrderSingle>'
perl -ne '/\h(SessionID=".*?")?(?:\h++.*(MsgType=".*?"))?\h/ and print "$1|$2\n"' <<< "$s"

这打印:

SessionID="kkk"|
SessionID="zkx"|MsgType="D"