Basically when you install multiple PHPs with Homebrew, they don't end up on PATH anywhere - you can brew link one of them, but that overwrites any other PHPs you might have previously linked. Other platforms, such as Ubuntu, package their PHPs such that a binary called something like php7.4 ends up on PATH. This is a much more helpful approach, since you can specifically invoke the necessary version of PHP by adding a version suffix. This script does the same thing for Homebrew-installed PHPs. Pretty simple.