Package Management

Ubuntu / Debian

dpkg -i <package>                   # Install a package from local file
dpkg --get-selections               # Show the list of packages installed through apt-get
dpkg --get-selections | grep php    # ... filtering for some specific package keyword
dpkg -L <package>                   # Show files delivered by a given <package>
apt-cache search <keyword>          # Search package cache (package name and description) for given <keyword>

To add a repository, edit file /etc/apt/sources.list ou sources.list.d/, then apt-get update.