It entirely depends on my use case. If I'm stringing I/O together from other applications, I'll just glue them together in Bash.
If I'm building something a bit more robust or integrated I'll use Python or Groovy or Node.
An example would be: we have a Java web app with some REST APIs for updating content. Instead of rebuilding the models, I just pulled the domain objects into a core library and wrote a Groovy CLI around it.