apt-cache

List all installed packages

# apt-cache pkgnames

List all installed packages starting with openssh

# apt-cache pkgnames openssh

Show real name of the package and show package description

# apt-cache search openssh

Show package information

# apt-cache show openssh

Show dependencies for specified package, whether they are installed or not

# apt-cache showpkg openssh

Show package’s dependencies

# apt-cache depends openssh

Show any unmet dependencies

# apt-cache unmet