we could do with an 'exec' which just executes the commands in a child process?
now we have fork, maybe we don't need "execjar" and "exec"?
names seem a bit inconsistent; we maybe need clearer names. e.g. fork, forkjar, forkrun maybe?
run - run java class
jar - run jar
exec - run arbitrary commands
then fork to fork a new jvm?
- fork <args>
- forkrun run a java class forked
- forkjar run a jar forked