How to change Ruby version for Homebrew in macOS in Travis CI?

Question

Trying to run

if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install python3; fi

in before_install, I end up with

/usr/local/Homebrew/Library/Homebrew/brew.rb:12:in \`<main>': Homebrew must be run under Ruby 2.3! (RuntimeError)  

The command "if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install python3; fi" failed and exited with 1 during .

Your build has been stopped.

/Users/travis/.travis/job_stages: line 166: shell_session_update: command not found  

So I assume the issue here is that ruby is on version 2.0, which I confirmed with ruby --version. The funny thing is, my builds just stopped working all of the sudden, without any change to .travis.yml.
So how do I actually change Ruby versions?

Might be important to not, that before git clone is run I get this:

$ rvm use

Warning! PATH is not properly set up, '/Users/travis/.rvm/gems/ruby-2.0.0-p648/bin' is not at first place,

         usually this is caused by shell initialization files - check them for 'PATH=...' entries,

         it might also help to re-add RVM to your dotfiles: 'rvm get stable --auto-dotfiles',

         to fix temporarily in this shell session run: 'rvm use ruby-2.0.0-p648'.

Answer 1

Your choices seem to be to either use

brew update
brew install whatever

or

HOMEBREW_NO_AUTO_UPDATE=1 brew install whatever

The advice in travis documentation to not do a brew update if it doesn't seem to be needed seems to leave you at risk of random breakage when brew's ruby requirement is changed...

Answer 2

running brew update before brew install package_name

Answer 3

• brew update
• brew install ruby-build
• brew install rbenv
• rbenv install [version_required]
• rbenv global [version_required]

Answer 4

For .NET Core projects: you can avoid using brew by not using Travis' default .NET Core but installing it using the Microsoft's .NET core sh script. I used to have mono and dotnet version definitions set which I've found were not needed after switching to the sh script. I was able to fix the Homebrew must be run under Ruby 2.3! error by removing those two definitions (although I then had to update libunwind8 on Linux before doing the .NET core install).

Here's the complete .travis.yaml for running .NET core project test on osx and linux.

language: csharp

before_install:
  - if [ "$OS" = "linux" ]; then sudo apt-get install libunwind8; fi

script:
  - wget https://dot.net/v1/dotnet-install.sh && chmod +x dotnet-install.sh
  - ./dotnet-install.sh --version 1.1.4 --install-dir $HOME/.dotnet
  - $HOME/.dotnet/dotnet restore
  - $HOME/.dotnet/dotnet test YOUR_CSPROJ_FILE_PATH

matrix:
  include:
    - os: linux
      dist: trusty
      env: OS=linux
    - os: osx
      osx_image: xcode9
      env: OS=osx

branches:
  only:
    - master