How to remove an event from logstash?
Just use a drop filter to drop any line that starts with ;:
filter { if ([message] =~ "^;") { drop {} }}Although based on your output, it really ;/r not ;\r, so you might need to adjust if your output is not just an example.
You can also just drop anything that fails to grok:
if "_grokparsefailure" in [tags] { drop {} }