pacman(1)

Remote package repositories

pacman -Sy              refresh package database
pacman -S <pkg>         install pkg
pacman -Ss <regex>      search remote package database
pacman -Si <pkg>        get info for pkg
pacman -Su              upgrade installed packages
pacman -Sc              clean local package cache

Remove packages

pacman -Rsn <pkg>               uninstall package and unneeded deps + config files

Local package database

Local package database of installed packages.

pacman -Q               list all installed packages
pacman -Qs <regex>      search local package database
pacman -Ql <pkg>        list files installed by pkg
pacman -Qo <file>       query package that owns file
pacman -Qe              only list explicitly installed packages

Local file database

Local file database which allows to search packages owning certain files. Also searches non installed packages, but database must be synced.

pacman -Fy              refresh file database
pacman -Fl <pkg>        list files in pkg (must not be installed)
pacman -Fx <regex>      search 

Hacks

Uninstall all orphaned packages (including config files) that were installed as dependencies.

pacman -Rsn $(pacman -Qqtq)

List explicitly installed packages that are not required as dependency by any package and sort by size.

pacman -Qetq | xargs pacman -Qi |
    awk '/Name/ { name=$3 }
         /Installed Size/ { printf "%8.2f%s %s\n", $4, $5, name }' |
    sort -h