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

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

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