Newbie Questions About The Homebrew Installation Script, Related To M1 Macs

[rdfuhr]

I have an M1 MacBook Pro, and I took a look at the current version (as of December 31, 2020) of the Homebrew installation script, which is located at https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh

I have not run this script, and have the following questions. Bear with me, since I am not fluent in this scripting language.

1. In this snippet of the script, the intention is to set HOMEBREW_PREFIX to "/opt/homebrew for arm64 Macs, but what is the meaning and the intent of the code that says if [[ -z "${HOMEBREW_ON_LINUX-}" ]]; then... in the following? Is the script to be interpreted that we will only execute the code to set HOMEBREW_PREFIX="/opt/homebrew" if HOMEBREW_ON_LINUX is false (and also of course that "$UNAME_MACHINE"=="arm64"?

if [[ -z "${HOMEBREW_ON_LINUX-}" ]]; then
if [[ "$UNAME_MACHINE" == "arm64" ]]; then
# On ARM macOS, this script installs to /opt/homebrew only
HOMEBREW_PREFIX="/opt/homebrew"

2. Does the user need to create the directory /opt/homebrew before running the script?

[carlocab]

what is the meaning and the intent of the code

You'll want to read man bash. In particular, you are looking for the sections on CONDITIONAL EXPRESSIONS and EXPANSION. You can also read about the equivalents for Zsh in man zshmisc and man zshexpn.

Does the user need to create the directory /opt/homebrew

No. The script will tell you everything you need to do when you run it. It also tells you everything it does as it runs.