How to use apt-cache under Ubuntu Linux

apt-cache performs a variety of operations on APT's package cache.  apt-cache does not manipulate the state of the system but does provide operations to search and generate interesting output from the package meta data.

showpkg displays information about the packages listed on the command line

apt-cache showpkg firefox

Stats displays some statistics about the cache

apt-cache stats

Dump shows a short listing of every package in the cache. It is primarily for debugging.

apt-cache dump firefox

Dumpavail prints out an available list to stdout

apt-cache dumpavail firefox

Unmet displays a summary of all unmet dependencies in the package cache.

apt-cache unmet firefox

Search the package list for a regex pattern

apt-cache search firefox

Show a readable record for the package

apt-cache show firefox

Depends shows a listing of each dependency a package has and all the possible other packages that can fulfill that dependency

apt-cache depends firefox

This command prints the name of each package APT knows.

apt-cache pkgnames 

Dotty takes a list of packages on the command line and generates output suitable for use by dotty from the GraphViz package.

apt-cache dotty firefox

Here 'firefox' is the package name used.