Using if-else with Logstash split - logstash

Question

I have a string field called description delimited with _.
I split it as follows:
filter {
mutate {
split => ["description", "_"]
add_field => {"location" => "%{[description][3]}"}
}
How can I check if the split values are empty or not?
I have attempted:
if !["%{[description][3]}"] {
# do something
}
if ![[description][3]] {
# do something
}
if ![description][3] {
# do something
}
None of them work.
The goal is to have the value of the new field location as its actual value or a generic value such as NA.

Answer 1

you made a really simple mistake with your mutate split.
this
mutate {
split => ["description", "_"]
add_field => {"location" => "%{[description][3]}"}
}
should have been
mutate {
split => ["description"=> "_"] <=== see I removed the comma and added =>
add_field => {"location" => "%{[description][3]}"}
}
here is sample I tested out with
filter {
mutate {
remove_field => ["headers", "#version"]
add_field => { "description" => "Python_Java_ruby_perl " }
}
mutate {
split => {"description" => "_"}
}
if [description][4] {
mutate {
add_field => {"result" => "The 4 th field exists"}
}
} else {
mutate {
add_field => {"result" => "The 4 th field DOES NOT exists"}
}
}
and the result on console (since there is no 4 th element, it went to else block
{
"host" => "0:0:0:0:0:0:0:1",
"result" => "The 4 th field DOES NOT exists", <==== from else block
"#timestamp" => 2020-01-14T19:35:41.013Z,
"message" => "hello",
"description" => [
[0] "Python",
[1] "Java",
[2] "ruby",
[3] "perl "
]
}