This script to updates Git and SVN repos (i.e. git pull & svn up) checked out in the same directory. This is primarily intended for WordPress Core development, specifically for these two repos:
Git: https://github.com/WordPress/wordpress-develop.git
SVN: https://develop.svn.wordpress.org/trunk/
Pass a branch name like 6.6 as the sole argument to check out that branch. Otherwise, trunk is checked out.
This script was originally developed in the GoogleChromeLabs/wordpressdev repo but was split into a separate repo via git-filter-repo.
Check out Felix Arntz's writeup: My WordPress Core Contribution Workflow.