"logstash output exec " no output

[pegasus-zhang]

i tried the exec plugin of logstash:
output {
exec {
codec => line { format => "%{message}"}
command => "echo %{message}"
}
}
but nothing print out , only shown:
[2019-10-30T22:18:42,715][INFO ][logstash.outputs.exec ][main]

why nothing printed ? (it can be sure that the "message" is not null)

[pegasus-zhang]

while message can be show using "stdout"
output {
stdout {
codec => line { format => "%{message}"}
}
}

why "exec" is invalid ?

[Badger]

Try enabling log.level debug

[pegasus-zhang]

now it works , thanks