Why i cant use if statement in grock block?

[RameshNagargoje]

I want to add if statement and check condition in grok block if grok pattern is matched and add module in given json.
Bellow Filter shows error please help.

   grok
   {
 
      match => { logs => "killed by TERM signal"}
      if ([boardname] =~ /^.*tester.*$/) 
      {
                add_field  => {"module" => "null"}
      }
   }

[RameshNagargoje]

@Jenni @magnusbaeck

[Christian_Dahlqvist]

You can not use conditionals within ANY filter definition. You can however place the conditional outside the grok filter block and use a mutate filter to add the field.

[RameshNagargoje]

thanks @Christian_Dahlqvist
Is this Correct way to do it?

 grok
{

  match => { logs => "killed by TERM signal"}
  add_tag => ["regexMatched"]
} 
if "regexMatched" in [tags]
{
        if ([boardname] =~ /^.*tester.*$/) 
       {
            add_field  => {"module" => "null"}
       }
}

[Christian_Dahlqvist]

Almost. When a grok filter fails to match any expression, it by default adds a _grokparsefailure tag, so you can trigger on this instead of adding a separate field if you want. You also need to wrap the add_field statement in a filter, e.g. mutate. Something like this should work:

grok {
  match => { "logs" => "killed by TERM signal"}
} 

if "_grokparsefailure" not in [tags] {
  if ([boardname] =~ /^.*tester.*$/) {
    mutate {
      add_field  => {"module" => "null"}
    }
  }
}

[RameshNagargoje]

thank you @Christian_Dahlqvist it worked.