apt

Debian/Ubuntu package manager

high risk

interactive breakdown — edit the command and press Explain
$ 
⚠ Risks & cautions
Safer / dry-run alternatives
apt install -s <pkg>Simulate
apt-mark showholdCheck held packages
What it does

High-level package tool: update, install, remove, upgrade, autoremove.

Common flags
FlagMeaning
updateRefresh the package index
installInstall
removeRemove packages (keep config)
purgeRemove packages and config⚠ Deletes configuration.
autoremoveRemove unused dependencies⚠ May remove things you still need.
-s-s⚠ Simulate
--dry-run --dry-runSimulate
Examples
apt list --upgradableWhat can be upgraded? · explain & risk-check →
apt install -s nginxSimulate · explain & risk-check →
Related
apt-get dpkg
Open the full explainer →More in Packages & Build

Reference text is hand-written and may be incomplete — check man apt for your version. Test destructive commands on a non-production system first.