zsh under MacOS uses the x86_64 binary

[nwin]

Output of brew config

HOMEBREW_VERSION: 4.3.9
ORIGIN: https://github.com/Homebrew/brew
HEAD: 1c98a33a376e5b35ebc801d0f7d6ba7b9eb118ac
Last commit: 9 days ago
Core tap JSON: 16 Jul 14:47 UTC
Core cask tap JSON: 16 Jul 14:47 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_REPOSITORY: /opt/homebrew
HOMEBREW_CELLAR: /opt/homebrew/Cellar
HOMEBREW_CASK_OPTS: []
HOMEBREW_EDITOR: /usr/local/bin/mate -w
HOMEBREW_MAKE_JOBS: 10
Homebrew Ruby: 3.3.3 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.3.3/bin/ruby
CPU: 10-core 64-bit westmere
Clang: 15.0.0 build 1500
Git: 2.39.3 => /Applications/Xcode.app/Contents/Developer/usr/bin/git
Curl: 8.6.0 => /usr/bin/curl
macOS: 14.5-x86_64
CLT: 15.3.0.0.1.1708646388
Xcode: 15.4
Rosetta 2: true

Output of brew doctor

Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry or file an issue; just ignore this. Thanks!

Warning: gettext files detected at a system prefix.
These files can cause compilation and link failures, especially if they
are compiled with improper architectures. Consider removing these files:
  [...]

Warning: Unbrewed '.la' files were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected '.la' files:
  [...]

Warning: Unbrewed '.pc' files were found in /usr/local/lib/pkgconfig.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected '.pc' files:
  [...]

Warning: Unbrewed static libraries were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected static libraries:
  [...]

Warning: Your Homebrew's prefix is not /usr/local.

Many of Homebrew's bottles (binary packages) can only be used with the default prefix.
Consider uninstalling Homebrew and reinstalling into the default prefix.
It is expected behaviour that some formulae will fail to build in this unsupported configuration.
It is expected behaviour that Homebrew will be buggy and slow.
Do not create any issues about this on Homebrew's GitHub repositories.
Do not create any issues even if you think this message is unrelated.
Any opened issues will be immediately closed without response.
Do not ask for help from Homebrew or its maintainers on social media.
You may ask for help in Homebrew's discussions but are unlikely to receive a response.
Try to figure out the problem yourself and submit a fix as a pull request.
We will review it but may or may not accept it.

Description of issue

When installing anything the following error message pops up

Error: Cannot install under Rosetta 2 in ARM default prefix (/opt/homebrew)!
To rerun under ARM use:
    arch -arm64 brew install ...
To install under x86_64, install Homebrew into /usr/local.

After some trying i figured that that when using bash it works. But not under zsh. For installing I used bash since this is what the install-Command uses. But for daily use I use zsh because that is what MacOS recommends.

I cannot figure out what is wrong with zsh, the architecture seems to be right.

 ~ % uname -m            
arm64
 ~ % uname -p
arm

brew config seems to indicate the problem macOS: 14.5-x86_64. But why? Any suggestions?

[gromgit]

What's the output of which brew? I'm betting you get /usr/local/bin/brew, which conflicts with all the Homebrew environment variables that were set up with eval "$(/opt/homebrew/bin/brew shellenv)" in your shell startup.

Check your PATH, you almost certainly have /usr/local/bin before /opt/homebrew/bin, likely because you added it after the brew shellenv line in your shell startup file.

[nwin]

I'm marking as answer since you gave me the clue. Thank you.

% which brew
brew: aliased to arch -x86_64 brew

Which I must have defined some time ago and forgotten about. I think I did it because I got the new computer and wanted to keep the old installation. The alias is defined in the .zshrc and the installation uses bash. When I now did a clean install it got completely mixed up.

[p-linnane]

At the bottom of the brew config you'll see Rosetta 2: true which also helps diagnose this.