Sass是一种css的开发工具，它的安装依赖Ruby，没有安装Ruby的请先安装Ruby。
假定你已经安装了Ruby，则可以直接执行如下语句进行安装。
gem install sass
常见错误提示：
1、ERROR: While executing gem ... (OpenSSL::SSL::SSLError)
hostname "gems.ruby-china.org" does not match the server certificate
解决办法：
执行命令，查看数据源
gem source -l
结果
*** CURRENT SOURCES *** https://ruby.taobao.org/ https://gems.ruby-china.org
则可以删除多余的
gem sources --remove https://ruby.taobao.org/ sudo gem update --system
然后重新安装。
2、ERROR: SSL verification error at depth 1: unable to get local issuer certificate (20)
ERROR: You must add /O=Digital Signature Trust Co./CN=DST Root CA X3 to your local trusted store
Fetching: ffi-1.9.18.gem ( 32%)ERROR: SSL verification error at depth 2: self signed certificate in certificate chain (19)
ERROR: Root certificate is not trusted (/C=US/O=GeoTrust Inc./CN=GeoTrust Global CA)
ERROR: While executing gem ... (OpenSSL::SSL::SSLError)
hostname "gems.ruby-china.org" does not match the server certificate
3、ERROR: SSL verification error at depth 1: unable to get local issuer certificate (20)
ERROR: You must add /O=Digital Signature Trust Co./CN=DST Root CA X3 to your local trusted store
Fetching: ffi-1.9.18.gem (100%)
Building native extensions. This could take a while...
Successfully installed ffi-1.9.18
ERROR: SSL verification error at depth 2: self signed certificate in certificate chain (19)
ERROR: Root certificate is not trusted (/C=US/O=GeoTrust Inc./CN=GeoTrust Global CA)
Fetching: rb-inotify-0.9.10.gem (100%)
Successfully installed rb-inotify-0.9.10
Fetching: sass-listen-4.0.0.gem (100%)
Successfully installed sass-listen-4.0.0
Fetching: sass-3.5.1.gem (100%)
ERROR: While executing gem ... (Errno::EPERM)
Operation not permitted - /usr/bin/sass
遇到以上错误 2和3的解决办法
sudo gem install -n /usr/local/bin sass
查看
sass -v
则会正确显示Sass版本号。
2017年12月28日更新：
Mac更新系统后，Ruby由2.0升级到2.3，再次使用Sass时候，发现报错。
于是决定升级SaaS，重新安装时遇到错误。最后找到解决方案：
先安装libgmp-dev，再重新安装即可。
brew install libgmp-dev sudo gem install -n /usr/local/bin sass