How do I match a newline in grok/logstash?

Adding the regex flag to the beginning allows for matching newlines:

match => [ "message", "(?m)%{TIMESTA...

My final grok for Vertica log using (?m) and [^\n]+

match => ["message","(?m)%{TIMESTAMP_ISO8601:ClientTimestamp}%{SPACE}(%{DATA:Action}:)?(%{DATA:ThreadID} )?(\[%{DATA:Module}\] )?(\<%{DATA:Level}\> )?(\[%{DATA:SubAction}\] )?(@%{DATA:Nodename}:)?( (?<Session>(\{.*?\} )?.*?/.*?): )?(?<message>[^\n]+)((\n)?(\t)?(?<StackTrace>[^\n]+))?"]

Thanks to asperla

https://github.com/elastic/logstash/issues/2282

All GREEDYDATA is is .*, but . doesn't match newline, so you can replace %{GREEDYDATA:message} with (?<message>(.|\r|\n)*)and get it to be truly greedy.