Install Gems Without sudo in macOS

I came across a neat little command line tool via Rob Griffiths’ Robservatory this morning, a Ruby gem named iStats¹. Install is easy enough in Rob’s example, sudo gem install iStats, except that when you use sudo to install gems you are using the default macOS Ruby, and installing to system paths.

➜  ~ /usr/bin/gem environment                            
RubyGems Environment:
RUBYGEMS VERSION: 2.0.14.1
RUBY VERSION: 2.0.0 (2015-12-16 patchlevel 648) [universal.x86_64-darwin16]
INSTALLATION DIRECTORY: /Library/Ruby/Gems/2.0.0
RUBY EXECUTABLE: /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
EXECUTABLE DIRECTORY: /usr/local/bin
RUBYGEMS PLATFORMS:
    ruby
    universal-darwin-16
GEM PATHS:
    /Library/Ruby/Gems/2.0.0
    /Users/jonathanbuys/.gem/ruby/2.0.0
    /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/gems/2.0.0
GEM CONFIGURATION:
    :update_sources => true
    :verbose => true
    :backtrace => false
    :bulk_threshold => 1000
REMOTE SOURCES:
    https://rubygems.org/

While that might be fine, my personal preference is to keep the core system as close to default as possible. I once ran into an issue keeping Jekyll up to date, so now I use the excellent Homebrew to install an updated version of Ruby and keep the gems in /usr/local, which is entirely mine and safe to write to.

brew install ruby

Also, I make sure that /usr/local/bin is called before /usr/bin in my shells PATH variable.

export PATH=/usr/local/bin:~/Unix/bin/:$PATH

Now I can call gem install iStats and the gems will be installed safely, keeping my core system clean and my gems easily updatable.