[SOLVED] What's the difference between these terminal commands?
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dpkg -l ( will list installed packages )
dpkg -list ( is not a valid option, use --list instead and will return the same output as -l )
dpkg --list | less ( less will allow you to page through the results if it is longer than a single page )
Yup, just use the grep command after a pipe. So something like dpkg --get-selections |grep uninstall. (or maybe it's not-installed. Also there's purge - which are files that were not just removed, but purged, i.e. their config files were also deleted).
Won't return anything, the reason being is that the cache does not list a package as uninstalled. The cache only has available packages and this list of available packages would have thousands of possibilities. Generally you would have somewhat of an idea as to what you are looking for. For example a search for openvpn would return the following results:
$ apt-cache search openvpn
openvpn-blacklist - list of blacklisted OpenVPN RSA shared keys
anytun - secure anycast tunneling protocol
ebox-openvpn - eBox - VPN Service
gadmin-openvpn-client - GTK+ configuration tool for openvpn (client)
gadmin-openvpn-client-dbg - GTK+ configuration tool for openvpn (debug for client)
gadmin-openvpn-server - GTK+ configuration tool for openvpn (server)
gadmin-openvpn-server-dbg - GTK+ configuration tool for openvpn (debug for server)
gadmintools - GTK+ server administration tools
kvpnc - vpn clients frontend for KDE4
network-manager-openvpn - network management framework (OpenVPN plugin)
network-manager-openvpn-gnome - network management framework (OpenVPN plugin, GNOME UI)
network-manager-openvpn-kde - KDE NetworkManagement infrastructure (OpenVPN plugin)
openvpn-auth-ldap - OpenVPN LDAP authentication module
tunneldigger - Configures OpenVPN tunnel networks
tunneldigger-utils - Utilities for TunnelDigger-configured OpenVPN tunnels
openvpn - virtual private network daemon
collectd-core - statistics collection and monitoring daemon (core system)
Notice that in this case openvpn is basically a search term not necessarily a package name. So it returns anything that has openvpn in the package description.