Filter on a number in a log catch

Elastic Stack Logstash
1

Hi,

I have a message

filebeat -- ERROR -- Nov 11 23:59:34 server25 smartd[12032]: Device: /dev/sda [SAT], SMART Prefailure Atribute: 1Raw_Read_Error_Rate changes from XX to YY

Where XX is a number and YY is a number i.e. "83 to 77" or "89 to 100"... Both are different most of the time, not just to each other, but to previous messages as well.
I keep getting this message multiple times a day and would like to only get it when YY drops below ... I guess about 50. I am very new to logstash how can I filter out only YY, change ERROR to WARNIG if it is above 50 and otherwise leave it unchanged if below 50.

Thanks

2

Use a grok filter to extract the numbers into separate fields, then wrap a conditional around additional filters that e.g. update the loglevel field or whatever it is you want to do.