See full tutorial here : https://cedricleruth.com/how-to-update-wordpress-core-version-from-unix-command-line-cli/

updateWordpressFromCommandLine.sh

#Your First need to install wordpress cli as describe : https://wp-cli.org/
#Try running 
wp help 

#and if you get an error run the following : 
curl -O https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar
php wp-cli.phar --info
#Should display system informations
#If there is no errors make it executable and move it to path :
chmod +x wp-cli.phar
sudo mv wp-cli.phar /usr/local/bin/wp
#You should now be able to run :
wp help

#Now that we have wp cli we can use it to update wordpress from command line
#You first need to know your wordpress installation path
locate wp-config.php
#e.g : /var/www/html/wp-config.php

#Then run the update command with the installation path you got above
wp core update --path='/var/www/html/'
#Success: WordPress is up to date.

#Bonus: you can then add it to your unix cron to be run once a week as follow : 
sudo crontab -e
#paste the following in a new line
30 5 * * 3 wp core update --path='/var/www/html/'
#wq!