Update Alternatives in Linux

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update-alternatives --query python
update-alternatives: error: no alternatives for python
sudo update-alternatives --install /usr/local/bin/python python `which python3.8` 2
# update-alternatives: using /usr/bin/python3.8 to provide /usr/local/bin/python (python) in auto mode

sudo update-alternatives --install /usr/local/bin/python python `which python2.7` 5
# update-alternatives: using /usr/bin/python2.7 to provide /usr/local/bin/python (python) in auto mode

update-alternatives --query python
# Name: python
# Link: /usr/local/bin/python
# Status: auto
# Best: /usr/bin/python2.7
# Value: /usr/bin/python2.7
# 
# Alternative: /usr/bin/python2.7
# Priority: 5
# 
# Alternative: /usr/bin/python3.8
# Priority: 2

sudo update-alternatives --install /usr/local/bin/python python `which python3.8` 20
# update-alternatives: using /usr/bin/python3.8 to provide /usr/local/bin/python (python) in auto mode