When running brew commands and interpreting the output, e.g. running
`brew livecheck --json`, it's necessary to stop other programs Homebrew
happens to execute from writing logging output to stdout. Most programs
don't do this, but `bundle install` does seem to.
To reproduce the issue you can run:
```shell
git -C "$(brew --prefix)" clean -ffdx Library/Homebrew/vendor
stdout=$(HOMEBREW_FORCE_VENDOR_RUBY=1 brew livecheck --newer-only --json --cask $(brew --repo homebrew/cask)/Casks/grid.rb)
echo "^^^ was stderr, >>> is stdout: $stdout"
```
If you run it without this change it will print a bunch of output like
this to the stdout before printing out the livecheck JSON output:
```text
Using bundler 1.17.3
Fetching byebug 11.1.3
Fetching coderay 1.1.3
Installing byebug 11.1.3 with native extensions
Installing coderay 1.1.3
Fetching colorize 0.8.1
Installing colorize 0.8.1
[
# Contents of the JSON block.
]
```
With this change the stdout from `bundle install` will be redirected to
brew's stderr, meaning only the JSON goes to stdout, and the rest goes
to stderr.
07d571bebc