Not able to run logstash first stash event

I installed latest logstash 7.8.1 to CentOS 7.8. I am not able to run first stash event:

[root@logstash]# bin/logstash -e 'input { stdin { } } output { stdout {} }'
hello world
^C

I don't know why. Please help! Thanks!

Xinhuan

I found it just takes a while for logstash to start. I waited enough time, then I was able to stash my first event!