sass --watch をしたら Listen will be polling for changes. Learn more at https://github.com/guard/listen#polling-fallback. となってしまった時の対応方法 ref: http://qiita.com/ponsuke0531/items/e3ddcacfa1edd43fad3f

file0.txt

$ sass --watch sass:css --sourcemap=none
>>> Sass is watching for changes. Press Ctrl-C to stop.
[Listen warning]:
  Listen will be polling for changes. Learn more at https://github.com/guard/listen#polling-fallback.
>>> Change detected to: sass/style.scss
      write css/style.css

file1.txt

$ sudo gem install listen
Password:
Fetching: rb-fsevent-0.9.8.gem (100%)
Successfully installed rb-fsevent-0.9.8
Fetching: ffi-1.9.18.gem (100%)
Building native extensions.  This could take a while...
Successfully installed ffi-1.9.18
Fetching: rb-inotify-0.9.10.gem (100%)
Successfully installed rb-inotify-0.9.10
Fetching: ruby_dep-1.5.0.gem (100%)
Successfully installed ruby_dep-1.5.0
Fetching: listen-3.1.5.gem (100%)
Successfully installed listen-3.1.5
Parsing documentation for rb-fsevent-0.9.8
Installing ri documentation for rb-fsevent-0.9.8
Parsing documentation for ffi-1.9.18
Installing ri documentation for ffi-1.9.18
Parsing documentation for rb-inotify-0.9.10
Installing ri documentation for rb-inotify-0.9.10
Parsing documentation for ruby_dep-1.5.0
Installing ri documentation for ruby_dep-1.5.0
Parsing documentation for listen-3.1.5
Installing ri documentation for listen-3.1.5
Done installing documentation for rb-fsevent, ffi, rb-inotify, ruby_dep, listen after 15 seconds
5 gems installed
$ sass --watch sass:css --sourcemap=none
>>> Sass is watching for changes. Press Ctrl-C to stop.
>>> Change detected to: sass/style.scss
      write css/style.css

file2.txt

$ sudo gem install listen
Password:
Fetching: rb-fsevent-0.9.8.gem (100%)
Successfully installed rb-fsevent-0.9.8
Fetching: ffi-1.9.18.gem (100%)
Building native extensions.  This could take a while...
Successfully installed ffi-1.9.18
Fetching: rb-inotify-0.9.10.gem (100%)
Successfully installed rb-inotify-0.9.10
Fetching: ruby_dep-1.5.0.gem (100%)
ERROR:  Error installing listen:
    ruby_dep requires Ruby version >= 2.2.5, ~> 2.2.
$ ruby -v
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]

file3.txt

$ gem install ruby <---- 自動で最新がインストールされるわけではなかった・・・
Fetching: ruby-0.1.0.gem (100%)
ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /Library/Ruby/Gems/2.0.0 directory.
$ sudo gem uninstall ruby <--------- 古いのをアンインストール
$ sudo gem install ruby <----------- 今一度インストール
Fetching: ruby-0.1.0.gem (100%)
Successfully installed ruby-0.1.0
Parsing documentation for ruby-0.1.0
Installing ri documentation for ruby-0.1.0
1 gem installed
$ ruby -v <--------------- バージョンが・・・上がらない・・・(ホントはここで新しいバージョンのrubyはインストールされていました。)
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]
$ brew doctor
Your system is ready to brew.
$ brew install ruby <------------ Homebrewでrubyをインストール
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 4 taps (caskroom/cask, homebrew/core, homebrew/php, homebrew/science).
==> New Formulae
<省略>
==> Updated Formulae
<省略>
==> Renamed Formulae
<省略>
==> Deleted Formulae
<省略>
==> Installing dependencies for ruby: libyaml
==> Installing ruby dependency: libyaml
==> Downloading https://homebrew.bintray.com/bottles/libyaml-0.1.7.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring libyaml-0.1.7.sierra.bottle.tar.gz
==> Using the sandbox
🍺  /usr/local/Cellar/libyaml/0.1.7: 8 files, 312.6KB
==> Installing ruby
==> Downloading https://homebrew.bintray.com/bottles/ruby-2.4.1_1.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring ruby-2.4.1_1.sierra.bottle.tar.gz
==> Caveats
Emacs Lisp files have been installed to:
  /usr/local/share/emacs/site-lisp/ruby
==> Summary
🍺  /usr/local/Cellar/ruby/2.4.1_1: 1,191 files, 15.5MB
$ ruby -v <------------- 2.4.1をインストールしたのに・・・
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]
$ which ruby <------------- パスが通っていない・・・・
/usr/local/bin/ruby
$ cd ~
mananoMacBookAir:~ mana$ vi .bashrc <---------- ターミナルでbashをつかっているので「.bashrc」でHomebrewのインストール場所へパス設定します
mananoMacBookAir:~ mana$ source .bashrc 
mananoMacBookAir:~ mana$ ruby -v　<------------ やっとバージョンが上がってListenをインストールできました。
ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-darwin16]

file4.txt

$ gem environment
RubyGems Environment:
  - RUBYGEMS VERSION: 2.6.11
  - RUBY VERSION: 2.4.1 (2017-03-22 patchlevel 111) [x86_64-darwin16]
  - INSTALLATION DIRECTORY: /usr/local/lib/ruby/gems/2.4.0
  - USER INSTALLATION DIRECTORY: /Users/mana/.gem/ruby/2.4.0
  - RUBY EXECUTABLE: /usr/local/opt/ruby/bin/ruby
  - EXECUTABLE DIRECTORY: /usr/local/bin
  - SPEC CACHE DIRECTORY: /Users/mana/.gem/specs
  - SYSTEM CONFIGURATION DIRECTORY: /usr/local/Cellar/ruby/2.4.1_1/etc
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-darwin-16
  - GEM PATHS:
     - /usr/local/lib/ruby/gems/2.4.0
     - /Users/mana/.gem/ruby/2.4.0
     - /usr/local/Cellar/ruby/2.4.1_1/lib/ruby/gems/2.4.0
  - GEM CONFIGURATION: