Generation of var/cache/ var/generation and var/di folders Magento2

Question

I have a very simple question. Which magento commands cause the removal of

var/cache/ 
var/generation/
var/di/

Folders and which bin/magento commands create them again.

• Prince Patel: You can prefer this answer for when you should run which commands: magento.stackexchange.com/a/184927/35758

Answer 1

var/cache is cleared by php bin/magento cache:flush. It rebuilds on the fly as data is cached by Magento (there's no command to rebuild, it just happens).

var/di and var/generation are cleared by php bin/magento setup:upgrade, or manually (like executing rm -rf var/di var/generation from site root--be very careful with this!). You can rebuild them by running the command php bin/magento setup:di:compile. If you are in non-production mode, you can leave them and Magento will rebuild the generated sources on the fly (but it'll be a little slower while that happens).

Answer 2

must be php bin/magento cache:flush command