How to Debug gremlin groovy script when load data to Titan

I'm new to titan and groovy. I wrote a groovy script to load data to titan, executed with ./bin/gremlin.sh -e load.groovy. When this script is running, it always throws Exception. Has there a way to debug when running gremlin groovy script? I'm really exhausted to write printf everywhere. Or another way to load data to titan with debugging?