Can't modify field after KV filter v6.3

[ryannelle]

Here is my sample data
msg=key,value key2,value1 key3,value2,value3 key4,value4

My kv filter works and I end up with the result below

"toplvl.midlvl" = { 
"key" => "value",
"key2" => "value1",
"key3" => "value2,value3",
"key4" => "value4"
}

So now I want to modify the value in key3 and remove value2 and the comma because I don't care about them. I just want value3 in that field.

I think I need to use gsub here

Blockquote gsub Match a regular expression against a field value and replace all matches with a replacement string.

mutate { gsub => [  "[toplvl][midlvl][key3]", "*,", "" ] }

It's not doing anything to the field
I even tried a rename of the field and that didn't work either.
I feel like I am not calling the field correctly but not sure why.

Please let me know if there is another way or if I am doing this incorrectly.
Thanks

[magnusbaeck (Magnus Bäck)]

I'd try to use [toplvl.midlvl][key3] to reference that field. Also, your regexp is wrong. Use e.g. .*, instead.

[ryannelle]

Thank you !!!.

That did the trick.