Debian / Ubuntu Linux search package names with apt-cache command

Q. I'd like to find out if xyz package is available or not using apt-get command. How do I look up package names and contents via shell command?

A. You need to use apt-cache command to 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 metadata.

apt-cache search {package} command

search option performs a full text search on all available package lists for the regex pattern given. It searches the package names and the descriptions for an occurrence of the regular expression and prints out the package name and the short description. For example search for lighttpd package, enter:
$ apt-cache search lighttpd
Output:

lighttpd - A fast webserver with minimal memory footprint
lighttpd-doc - Documentation for lighttpd
lighttpd-mod-cml - Cache meta language module for lighttpd
lighttpd-mod-magnet - Control the request handling module for lighttpd
lighttpd-mod-mysql-vhost - MySQL-based virtual host configuration for lighttpd
lighttpd-mod-trigger-b4-dl - Anti-deep-linking module for lighttpd
lighttpd-mod-webdav - WebDAV module for lighttpd
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