Bash Tokenization Errors on Jenkins JNLP Slave
I cannot say this is a the best answer so I do hope someone can provide a better clarification.  

It seems the default shell for sh() in Jenkins is Bourne.  By updating the sh() with the correct shell this allows the below usage:

sh'''#!/bin/bash
    IFS='/'
    branch=($1)
    # Use it.
'''


This doesn't resolve the the redirection error.  Also I would think by updating the default shell in the image with chsh -s /bin/bash I wouldn't need to set it but I still do.