查看所有的变量：

$ printenv
PATH=/Library/Frameworks/Python.framework/Versions/3.4/bin:/Users/calios/.cabal/bin:/Applications/ghc-7.8.4.app/Contents/bin:/Library/Frameworks/Python.framework/Versions/3.4/bin:/Users/calios/.cabal/bin:/Applications/ghc-7.8.4.app/Contents/bin:/Library/Frameworks/Python.framework/Versions/3.4/bin:/Users/calios/.cabal/bin:/Applications/ghc-7.8.4.app/Contents/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin
ZSH=/Users/calios/.oh-my-zsh


查看指定的变量：

$ echo $SHELL
/bin/zsh

设置临时环境变量

$ export PATH=$PATH:~/bin

后面的$PATH意味着在原有值的基础上，拼接上~/bin/，再将新值赋给PATH。