What is the grok expression that can match variable length documents from a single log file?

Elastic Stack Logstash
1

A log file is having records of different leighths, say 3 different types of records?
what is the grok expression that can match variable length documents from a single log file?

This will be very useful for creating index and ingest node for it via the interface provided by kibana (upload sample file)

regards
shini

2

This is really hard to answer without any example data. grok matches fields regular expressions. A regexp can match literally anything.