I need to parse this log message format

[A_B]

@Tanya_Sharma

< filter {
grok{
match => { "message" => "[%{TIMESTAMP_ISO8601:logdate}[%{LOGLEVEL:LEVEL}][%{GREEDYDATA:errormsg}]" }
}
}
/>

did you actually get Logstash to start with that config? Logstash is usually very picky about config file syntax (well, which program isn't). The special character </> need to be within a filer definition. You can see my example above