To manage packages:
To show help of "apt" command:
apt help
To display policy:
apt policy
To update package information, upgrade installed packages and install necessary dependencies:
sudo apt update && sudo apt dist-upgrade
To install a package ("-y" below is optional. It simply says "yes".):
sudo apt -y install [package]
To upgrade a package:
sudo apt upgrade [package]
To upgrade a package and install new dependencies if necessary:
sudo apt dist-upgrade [package]
To overwrite an installed old version without upgrading:
sudo apt install [package] --no-upgrade
To remove a package without removing configuration files:
sudo apt remove [package] && sudo apt autoremove
To remove a package together with configuration files:
sudo apt purge [package]
To remove a package, unused packages, and configs:
sudo apt --purge autoremove [package]
To remove old downloaded archive files:
sudo apt autoclean
[apt autoclean removes the retrieved packages from the local cache only while the apt-get autoremove removes the unneeded packages that were once installed as a dependency.]
To list installed packages:
apt list --installed
To check if a package or packages is/are installed, for examples:
apt -qq list fcitx-frontend-qt5
apt -qq list fcitx-frontend*
To list upgradable packages:
apt list --upgradable
To show a package information:
apt show [package]
TO show a package dependency:
apt depends [package]
To search for a package, e.g.:
apt search fcitx
OR
apt-cache search fcitx