when I add a custom pattern wich starts with "(?<"， I run into "error parsing regexp: invalid or unsupported Perl syntax: (?<"

[arloor]

I searched golang docs. And I found this description:

So I changed my custom pattern to "(?P<":

(?P<loglevel>[A-Z])%{NUMBER:logdate} %{TIME:logtime}%{SPACE}%{NUMBER:threadid} (?P<file_source>%{WORD}\.%{WORD}):(?P<file_line>%{NUMBER})\]%{SPACE}GetBucket\[token:%{NOTSPACE:token}, path:%{URIPATHPARAM:request}\]

But I notice that the default patterns are no need to start with "(?P<", indeed they start with "(?<":

CLOUDFRONT_ACCESS_LOG (?<timestamp>%{YEAR}-%{MONTHNUM}-%{MONTHDAY}\t%{TIME})\t%{WORD:x_edge_location}\t(?:%{NUMBER:sc_bytes:int}|-)\t%{IPORHOST:clientip}\t%{WORD:cs_method}\t%{HOSTNAME:cs_host}\t%{NOTSPACE:cs_uri_stem}\t%{NUMBER:sc_status:int}\t%{GREEDYDATA:referrer}\t%{GREEDYDATA:agent}\t%{GREEDYDATA:cs_uri_query}\t%{GREEDYDATA:cookies}\t%{WORD:x_edge_result_type}\t%{NOTSPACE:x_edge_request_id}\t%{HOSTNAME:x_host_header}\t%{URIPROTO:cs_protocol}\t%{INT:cs_bytes:int}\t%{GREEDYDATA:time_taken:float}\t%{GREEDYDATA:x_forwarded_for}\t%{GREEDYDATA:ssl_protocol}\t%{GREEDYDATA:ssl_cipher}\t%{GREEDYDATA:x_edge_response_result_type}