Beanshell starts up pretty quickly. Besides, Bash scripts take an eternity to write safely and aren't really suitable for any sort of heavy calculations or string manipulation without resorting to arcane syntax. I would say it's an all-around good alternative to Python scripts when one outgrows Bash due to requirements.

I have also written some shellscripts in java (i did not smoke anything). If startuptime would be an issue (normally it is not) i would just use graal-vm to compile it. Just do this: "native-image script"