Ruby – Error Message “Xcode alone is not sufficient on Sierra”

command-line-toolhomebrewpython-3.xrubyxcode

I'd like to install openCV to vectorize image, but there's a series error message regarding Xcode and Ruby.

First, I use terminal to install openCV, brew install opencv.

Then, I got error message indicating that the system doesn't like my ruby version.

/usr/local/Homebrew/Library/Homebrew/brew.rb:12:in `<main>': 
Homebrew must be run under Ruby 2.3! You're running 2.0.0. (RuntimeError)

So, I want to upgrade my ruby. I followed several update strategy from this post. First ruby upgrade trial: brew link --overwrite ruby & brew unlink ruby && brew link ruby and get

Error: No such keg: /usr/local/Cellar/ruby

Then second ruby upgrade trial: brew upgrade ruby and see the following error message. 

Error: Xcode alone is not sufficient on Sierra.
Install the Command Line Tools:
xcode-select --install

This error message means I need to install Xcode which I already install. So, I check my Xcode status with code-select -p and get /Applications/Xcode.app/Contents/Developer which means I am fine.

I saw a comment regarding where you install python could be a big issue. Quote from the source:

If you see /usr/local/bin/python3 then you are correctly using the Homebrew version of Python. If the output is instead /usr/bin/python3 then you are incorrectly using the system version of Python.

I check which python3 and get

/Users/******/anaconda3/bin/python3

Could this be the problem? How can I change system version to local?

Best Answer

Let me explain this myself so people won't make the same mistakes.

When I saw the last line of the error message 

Error: Xcode alone is not sufficient on Sierra.
Install the Command Line Tools:
xcode-select --install

My thought was: I already have Xcode why the system ask me to "reinstall" it. However, thanks for @SamiKuhmonen @ Beartech @patrick kuang suggestion, I search a page (in Mandarin). xcode-select --install does not reinstall the whole Xcode. It means install some missing command line tools which is required by installing Ruby.

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