Find the actual arch (arm64 or i386) of a Mac, even if running in Rosetta

arch.sh

## Note - this should work in bash and zsh scripts

ARCH=$(sysctl kern.version | awk -F'_' '/RELEASE/{print $2}')

if [[ "$ARCH" == "ARM64" ]]
then
	ARCH='arm64'
elif [[ "$ARCH" == "X86" ]]
then
	ARCH='i386'
else
	echo "Unknown arch returned: '$ARCH'" >>/dev/stderr 
	exit 2
fi

echo "$ARCH"

An Alternative Method: I don't prefer this way, but it is another option:

sysctl kern.version | fgrep -q '/RELEASE_ARM64_'

EXIT="$?"

if [[ "$EXIT" == "0" ]]
then
	ARCH='arm64'
else
	ARCH='i386'
fi

What problem is this trying to solve: Normally you would use the arch command to tell if your Mac is 'i386' or 'arm64'. However, your script (or even your Terminal.app) might be running under Rosetta (for example, as of 2020-12-28 that is the recommended way to run brew), which would make it appear that you are on i386 even when you are on 'arm64'.

When trying to download Mac apps that offer separate versions for Intel or ARM (M1/Apple Silicon), you probably want the ARM version, even if your terminal program is running under Rosetta.