~/NetBeansProjects/jruby ➔ cat test.rb
puts 1
puts 2
puts 3

~/NetBeansProjects/jruby ➔ jruby --jdb test.rb
Initializing jdb ...
> stop at test:1
Deferring breakpoint test:1.
It will be set after the class is loaded.
> use .
> run
run org.jruby.Main test.rb
Set uncaught java.lang.Throwable
Set deferred uncaught java.lang.Throwable
> 
VM Started: Set deferred breakpoint test:1

Breakpoint hit: "thread=main", test.__file__(), line=1 bci=13
1    puts 1

main[1] list
1 => puts 1
2    puts 2
3    puts 3
4    
main[1] next
> 1

Step completed: "thread=main", test.__file__(), line=2 bci=37
2    puts 2

main[1] next
> 2

Step completed: "thread=main", test.__file__(), line=3 bci=61
3    puts 3

main[1] list
1    puts 1
2    puts 2
3 => puts 3
4    
main[1] cont
> 3

The application exited