upgrade bash to v4.2 on MAC

# prerequisite: gcc
# installation steps

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# download

curl https://ftp.gnu.org/gnu/bash/bash-4.2.tar.gz -o ~/Downloads/bash42.gz
tar xzf ~/Downloads/bash42.gz

# using make to compile

cd ~/Downloads/bashr42
./configure && make && sudo make install

# using new shell

chsh -s /usr/local/bin/bash {user_name}
sudo bash -c "echo /usr/local/bin/bash >> /private/etc/shells"

# replace the old shell with the new one

sudo mv /bin/bash /bin/bash3.2.58
sudo ln -s /usr/local/bin/bash /bin/bash