参考
注意
对于 .bash_profile 文件的修改，终端需要重新打开，在执行命令，才能看到修改生效的结果。
实践
open ~/.bash_profile
打开这个文件.bash_profile，内容如下
# Setting PATH for Python 3.6
# The original version is saved in .bash_profile.pysave
PATH="/Library/Frameworks/Python.framework/Versions/3.6/bin:${PATH}"
export PATH
PATH="/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/bin:${PATH}"
export PATH
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm" # Load RVM into a shell session *as a function*
# added by Anaconda3 5.1.0 installer
export PATH="/Users/hncy-ios/anaconda3/bin:$PATH"
从上往下看，依次是自己安装的3.6版本的Python
/Library/Frameworks/Python.framework/Versions/3.6
安装的anaconda3的Python版本
/Users/hncy-ios/anaconda3
此时没有看到系统自带的Python版本，终端执行python，可以看到：
wxxdemac-mini:~ hncy-ios$ python
Python 3.6.4 |Anaconda, Inc.| (default, Jan 16 2018, 12:04:33)
[GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
终端执行python3，可以看到：
Python 3.6.4 |Anaconda, Inc.| (default, Jan 16 2018, 12:04:33)
[GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
看来是安装了anaconda3，环境配置覆盖了系统默认的Python版本，试着这样注释.bash_profile文件最后一行：
#export PATH="/Users/hncy-ios/anaconda3/bin:$PATH"
重新打开终端
终端执行python，可以看到：
Python 2.7.10 (default, Oct 6 2017, 22:29:07)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
很棒，原来的环境回来了。
那么，系统默认安装路径是在哪里？
通过这样：
>>> import sys
>>> print('\n'.join(sys.path))
/Library/Python/2.7/site-packages/pip-9.0.3-py2.7.egg
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python27.zip
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-darwin
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac/lib-scriptpackages
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-old
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-dynload
/Library/Python/2.7/site-packages
/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python
/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/PyObjC
>>>
可以看到，这个就是系统默认Python的安装路径
/System/Library/Frameworks/Python.framework/Versions/2.7
至于这个路径在哪里配置呢，文件 .bash_profile 中第二行注释是这么写的：
# The original version is saved in .bash_profile.pysave
尝试打开这个文件 .bash_profile.pysave，发现找不到这个文件，为啥？
wxxdemac-mini:~ hncy-ios$ open ~/.bash_profile.pysave
The file /Users/hncy-ios/.bash_profile.pysave does not exist.
既然知道了系统默认Python的安装路径，修改这个文件.bash_profile 如下：
# Setting PATH for Python 3.6
# The original version is saved in .bash_profile.pysave
PATH="/Library/Frameworks/Python.framework/Versions/3.6/bin:${PATH}"
export PATH
PATH="/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/bin:${PATH}"
export PATH
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm" # Load RVM into a shell session *as a function*
# added by Anaconda3 5.1.0 installer
export PATH="/Users/hncy-ios/anaconda3/bin:$PATH"
export PATH="/System/Library/Frameworks/Python.framework/Versions/2.7/bin:$PATH"
重新打开终端
执行python，如下：
wxxdemac-mini:~ hncy-ios$ python
Python 2.7.10 (default, Oct 6 2017, 22:29:07)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
为什么会这样呢？
原来终端的python命令响应，通过这个文件 .bash_profile 去寻找，而且是从下往上寻找。
如果我将 .bash_profile 文件中的关于Python的路径都注释：
# Setting PATH for Python 3.6
# The original version is saved in .bash_profile.pysave
#PATH="/Library/Frameworks/Python.framework/Versions/3.6/bin:${PATH}"
#export PATH
PATH="/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/bin:${PATH}"
export PATH
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm" # Load RVM into a shell session *as a function*
# added by Anaconda3 5.1.0 installer
#export PATH="/Users/hncy-ios/anaconda3/bin:$PATH"
#export PATH="/System/Library/Frameworks/Python.framework/Versions/2.7/bin:$PATH"
重新打开终端
发现：
wxxdemac-mini:~ hncy-ios$ python
Python 2.7.10 (default, Oct 6 2017, 22:29:07)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()
wxxdemac-mini:~ hncy-ios$ python3
Python 3.6.1rc1 (default, Mar 4 2017, 22:58:58)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
哈哈哈，我奔溃/::)。
echo $PATH
- 执行echo $PATH，可以看到当前运行的所有环境变量。
- shell在搜索时先搜索PATH环境变量中的第一个目录，没找到再接着搜索，如果找到则执行它，不会再继续搜索。
接着上面，注释 .bash_profile 文件中的所有关于Python的路径配置。终端执行echo $PATH，可以看到：
wxxdemac-mini:~ hncy-ios$ echo $PATH
/Users/hncy-ios/.rvm/gems/ruby-2.2.2/bin:/Users/hncy-ios/.rvm/gems/ruby-2.2.2@global/bin:/Users/hncy-ios/.rvm/rubies/ruby-2.2.2/bin:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
打印出来的是环境变量，每个环境变量用冒号:分开了，也就是有如下的环境变量：
/Users/hncy-ios/.rvm/gems/ruby-2.2.2/bin
/Users/hncy-ios/.rvm/gems/ruby-2.2.2@global/bin
/Users/hncy-ios/.rvm/rubies/ruby-2.2.2/bin
/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/bin
/usr/local/bin
/usr/bin:
/bin:/usr/sbin
/sbin
解开文件 .bash_profile 中关于anaconda3的路径的注释：
# Setting PATH for Python 3.6
# The original version is saved in .bash_profile.pysave
#PATH="/Library/Frameworks/Python.framework/Versions/3.6/bin:${PATH}"
#export PATH
PATH="/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/bin:${PATH}"
export PATH
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm" # Load RVM into a shell session *as a function*
# added by Anaconda3 5.1.0 installer
export PATH="/Users/hncy-ios/anaconda3/bin:$PATH"
#export PATH="/System/Library/Frameworks/Python.framework/Versions/2.7/bin:$PATH"
再次打开终端运行echo $PATH，发现：
wxxdemac-mini:~ hncy-ios$ echo $PATH
/Users/hncy-ios/anaconda3/bin:/Users/hncy-ios/.rvm/gems/ruby-2.2.2/bin:/Users/hncy-ios/.rvm/gems/ruby-2.2.2@global/bin:/Users/hncy-ios/.rvm/rubies/ruby-2.2.2/bin:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/hncy-ios/.rvm/bin
很明显，多了这个环境变量：
/Users/hncy-ios/anaconda3/bin
查看当前python的环境变量：
wxxdemac-mini:~ hncy-ios$ which python
/Users/hncy-ios/anaconda3/bin/python
这可以看出：
-
anaconda3的环境变量，是通过修改.bash_profile文件，达到动态添加到PATH中。 - 而Mac自带版本号为
2.7的python环境，和后来安装的版本为3.6的python环境，各自的环境变量如下，他们的环境变量是固定存在PATH中，所以就算注释掉.bash_profile文件中的配置，终端仍然可以执行。
wxxdemac-mini:~ hncy-ios$ which python
/usr/bin/python
wxxdemac-mini:~ hncy-ios$ which python3
/usr/local/bin/python3
也就是：
/usr/bin
/usr/local/bin
关于Mac下环境变量的配置
- 系统级别
/etc/profile
/etc/paths
- 用户级别
~/.bash_profile
~/.bash_login
~/.profile
~/.bashrc
