Not clear how define grok pattern

[mirkoperillo]

It's not clear how to define a custom grok pattern to debug it.

Indications says that One per line, the syntax for a grok pattern is %{SYNTAX:SEMANTIC}, but it's not the truth. The correct way is follow what it's declared in http://grokconstructor.appspot.com/do/match so On each line you give a pattern name, a space and the pattern