How can I run two isolated installations of Homebrew? - homebrew

Question

I want to install and run two versions of Homebrew simultaneously on an Apple Silicon Mac: an ARM64 version, and an Intel version running under Rosetta 2.
I know I can prepend any brew command with arch --x86_64 to emulate Intel for that command, but this can lead to conflicts for formulas whose dependencies you already have built for ARM64. For example:
Error: gnupg dependencies not built for the x86_64 CPU architecture:
pkg-config was built for arm64
gettext was built for arm64
readline was built for arm64
openssl#1.1 was built for arm64
How can I install and run two separate, isolated versions of Homebrew (one for native ARM64 and one for emulated Intel), keeping each of their installed formulae and dependencies separate?

Answer 1

Install Homebrew natively on Apple Silicon (will install to /opt/homebrew by default):
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
Install Intel-emulated Homebrew (will install to /usr/local by default):
arch --x86_64 /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
If you haven't yet installed Rosetta 2, you'll need to run softwareupdate --install-rosetta first.
Create an alias for Intel homebrew. I'm calling mine brow because O for old. But hey you do your own thing.
In ~/.zshrc (or your shell's equivalent) add:
alias brow='arch --x86_64 /usr/local/Homebrew/bin/brew'
Add ARM Homebrew to your PATH.
In ~/.zshrc (or your shell's equivalent) add:
# Homebrew on Apple Silicon
path=('/opt/homebrew/bin' $path)
export PATH
If you're still on bash it'd be PATH=/opt/homebrew/bin:$PATH
Confirm
which brew should return /opt/homebrew/bin/brew
brew --prefix should return /opt/homebrew
which brow should return brow: aliased to arch --x86_64 /usr/local/Homebrew/bin/brew
brow --prefix should return /usr/local
If you have the same command installed in both Homebrews, it'll default to Apple Silicon (/opt/homebrew/) since we prepended that one in our PATH. To override, run the command with its full path (/usr/local/bin/youtube-dl), or override your PATH for one command (PATH=/usr/local/bin youtube-dl).
I also created another handy alias in .zshrc (alias ib='PATH=/usr/local/bin') so I can prepend any Homebrew-installed command with ib to force using the Intel version of that command:
~ ▶ which youtube-dl
/opt/homebrew/bin/youtube-dl
~ ▶ ib which youtube-dl
/usr/local/bin/youtube-dl
If you prefer Intel to be the default brew, add /opt/homebrew/bin to the end of your PATH instead of the beginning.

Answer 2

Install Native Homebrew
❯ arch --arm64 zsh -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"
all Homebrew related stuffs are in /opt/homebrew.
Install Rosetta Homebrew
❯ arch --x86_64 zsh -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"
all Homebrew related stuffs are in /usr/local.
Configuring ~/.zshrc to use Brew defaultly based on arch,
# Multiple Homebrews on Apple Silicon
if [ "$(arch)" = "arm64" ]; then
eval "$(/opt/homebrew/bin/brew shellenv)"
export PATH="/opt/homebrew/opt/python#3.8/bin:$PATH"
# export LDFLAGS="-L/opt/homebrew/opt/python#3.8/lib" # For compilers to find python#3.8
else
eval "$(/usr/local/bin/brew shellenv)"
export PATH="/usr/local/opt/python#3.7/bin:$PATH"
export PATH="/usr/local/opt/python#3.9/bin:$PATH"
# export LDFLAGS="-L/usr/local/opt/python#3.7/lib" # For compilers to find python#3.7
fi
Test
❯ arch
arm64
❯ which brew
/opt/homebrew/bin/brew
❯ arch -x86_64 zsh
❯ arch
i386
❯ which brew
/usr/local/bin/brew
# set alias as you like
❯ rzsh='arch -x86_64 zsh'