Installing Ruby gems not working with Homebrew

Question

The gems I install via `sudo gem install ...` can't be executed (I get a `command not found`). They seem to install into `/usr/local/Cellar/` which is Brew's install directory (also, the gems in `/Library/Ruby/` don't work either). Is there anything else I need to do to make the gems executable? I'm using Zsh on Mac OS X 10.6 with Ruby v1.8 for the one in Brew. EDIT: It seems to be working now. I just went out for a few hours and came back to try it again.

Accepted Answer

Homebrew is nice. However unlike `brew` and `npm`, `gem` does not make aliases in `/usr/local/bin` automatically.

Solution

I went for a very simple approach (as of March 2020):

```
# Based on "`brew --prefix ruby`/bin"
export PATH=/usr/local/opt/ruby/bin:$PATH
# Based on "`gem environment gemdir`/bin"
export PATH=/usr/local/lib/ruby/gems/3.0.0/bin:$PATH
```

Add this to your `.bashrc` (or `.bash_profile`, `.zshrc`, etc.).

That's it! Now all Ruby bins and installed gems will be available from your shell!

In older versions of Homebrew (before 2017), there was a separate package for Ruby 2 called `ruby20`, for which you'd use the following snippet instead:

```
export PATH=/usr/local/opt/ruby20/bin:$PATH
```

This line was the only line needed at the time. But, in Ruby 2.1 the gems got moved to a separate directory. No longer under `/usr/local/opt/ruby/bin`, but instead at `/usr/local/lib/ruby/gems/2.0.0/bin` (where "2.0.0" is the last major Ruby version for Gem's purposes).

How it works

Homebrew keeps track of where it installed a package, and maintains a symbolic link for you that points there.

```
$ brew --prefix ruby
/usr/local/opt/ruby

$ l /usr/local/opt/ruby
/usr/local/opt/ruby@ -> ../Cellar/ruby/2.5.3_1
```

Effectively, adding `/usr/local/opt/ruby` to `PATH` is the same as the following:

```
export PATH=/usr/local/Cellar/ruby/2.5.3_1/bin:$PATH
```

Except, this long version hardcodes the currently installed version of Ruby and would stop working next time you upgrade Ruby.

As for Gem, the following command will tell you the exact directory Gem adds new packages to:

```
$ gem environment gemdir
/usr/local/lib/ruby/gems/2.7.0
```

Tools

These tools were meant to automatically bridge between Homebrew and Gem:

- josh/brew-gem (no longer exists)

- indirect/brewbygems (unmaintained)

I haven't used these but they might work for you.

Installing Ruby gems not working with Homebrew

Solution

Problem