dpkg
e apt-get
são duas maneiras diferentes de instalar o software. Basicamente, o apt-get, o aptitude e o synaptic são construídos sobre o programa de gerenciamento de pacotes dpkg do debian. Todos eles executam a mesma função básica - gerenciamento de pacotes, mas possuem alguns recursos extras. Um dos recursos extras do apt-get é que ele instalará dependências e o dpkg não.
Sobre o -p / purge ...
O -P
em dpkg
significa --purge
e removerá tudo, incluindo configurações e arquivos de configuração. Do manual:
-r, --remove, -P, --purge package...|-a|--pending
Remove an installed package. -r or --remove remove everything
except conffiles. This may avoid having to reconfigure the pack‐
age if it is reinstalled later. (Conffiles are configuration
files that are listed in the DEBIAN/conffiles control file). -P
or --purge removes everything, including conffiles. If -a or
--pending is given instead of a package name, then all packages
unpacked, but marked to be removed or purged in file
/var/lib/dpkg/status, are removed or purged, respectively. Note:
some configuration files might be unknown to dpkg because they
are created and handled separately through the configuration
scripts. In that case, dpkg won't remove them by itself, but the
package's postrm script (which is called by dpkg), has to take
care of their removal during purge. Of course, this only applies
to files in system directories, not configuration files written
to individual users' home directories.
Removing of a package consists of the following steps:
1. Run prerm script
2. Remove the installed files
3. Run postrm script
O mesmo vale para purge
em apt-get
.
remove
remove is identical to install except that packages are removed
instead of installed. Note the removing a package leaves its
configuration files in system. If a plus sign is appended to the
package name (with no intervening space), the identified package
will be installed instead of removed.
purge
purge is identical to remove except that packages are removed and
purged (any configuration files are deleted too).
Basicamente, é a mesma opção. Lembre-se: a remoção de dependências não acontece com o dpkg. O apt-get remove as dependências
Documentação do comentário de Lekensteyn: