环境变量
########


Linux::

    $ echo $SHELL
    /bin/zsh

    // HISTSIZE is the maximum number of lines that are kept in a session
    $ echo $SAVEHIST
    10000
    // SAVEHIST is the maximum number of lines that are kept in the history file. 
    $ echo $HISTFILE
    /Users/zhaoweiguo/.zsh_history
    // HISTFILE is the file name where your system is saving history.
    $ echo $HISTSIZE
    50000

oh-my-zsh::

    $ echo $ZSH
    /Users/zhaoweiguo/.oh-my-zsh
    $ echo $ZSH_CUSTOM
    /Users/zhaoweiguo/.oh-my-zsh/custom