First launch fails with Unknown command: brew PROMPT_SUBST

[chrismessina]

Before submitting

• I have searched the issues and pull requests for duplicates.
• I am reporting a specific problem with BrewUI and have described how to reproduce it, or the circumstances of an intermittent failure.

What happened?

After downloading, installing, and launching BrewUI for the first (and subsequent) times, the Installed screen fails to load. Instead of showing installed packages, it displays Homebrew’s command usage text and this error:

Error: Invalid usage: Unknown command: brew PROMPT_SUBST

The app shows “0 packages” and offers a Retry button, but the error remains.

Configuration and Upgrades show similar errors:

Doctor provides a diagnosis:

Expected behaviour

BrewUI should load the locally installed Homebrew packages.

If the installed Homebrew version or shell configuration is unsupported, BrewUI should detect that condition and show a clear, actionable compatibility message rather than exposing raw brew command output.

Steps to reproduce

1. Download and install BrewUI via homebrew.
2. Launch BrewUI for the first time.
3. Open the default Installed screen.

App version and build

Version 0.4.1 (1070)

How was the app installed?

Homebrew cask

macOS version and build

26.6.2-arm64

Mac processor

Apple silicon

Homebrew configuration

HOMEBREW_VERSION: 7.0.1-11-gd2c0312
ORIGIN: https://github.com/Homebrew/brew
HEAD: d2c031219d1cbe8a2b5bda4dcd8d7d9226151b1e
Last commit: 2 hours ago
Branch: main
Core tap: N/A
Core cask tap: N/A
HOMEBREW_PREFIX: /opt/homebrew
Homebrew Ruby: 4.0.6 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/4.0.6_2/bin/ruby
CPU: 16-core 64-bit arm_palma
Clang: 21.0.0 build 2100
Git: 2.50.1 => /Applications/Xcode.app/Contents/Developer/usr/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.6.2-arm64
CLT: 27.0.0.0.1788430756
Xcode: 26.6
Metal Toolchain: 17.0 (17F109)
Rosetta 2: false

Logs, screenshots and crash reports

See above.

Additional context

No response

[jbdamiano]

same issue with another error message

Example usage:
  brew search TEXT|/REGEX/
  brew info [FORMULA|CASK...]
  brew install FORMULA|CASK...
  brew update
  brew upgrade [FORMULA|CASK...]
  brew uninstall FORMULA|CASK...
  brew list [FORMULA|CASK...]

Troubleshooting:
  brew config
  brew doctor
  brew install --verbose --debug FORMULA|CASK

Contributing:
  brew create URL [--no-fetch]
  brew edit [FORMULA|CASK...]

Further help:
  brew commands
  brew help [COMMAND]
  man brew
  https://docs.brew.sh

Error: Invalid usage: Unknown command: brew fish_emoji_width