file * is better than ls -l,well sometimes

Yes file * will show all files with their types in the current directory,very useful sometimes.

Aptitude in Debian 5

dpkg -l shows all packages

dpkg -l | grep -i ssh will search for installed package ssh,the search will be case insentisitive

netstat -ntl | grep 22 will find the service that runs on 22 which is ssh

dpkg -L package name will show the contents of the package

dpkg -L openssh-client

when executing commnd such as dpkg -L openssh-client ,/usr/bin/scp will be shown in the results.so scp is a member package of openssh-client

if someone wants to find out which package belongs to which

dpkg -S /usr/bin/scp

will result in 

openssh-client

to install a package

dpkg - i packagename.deb

to remove a package

dpkg -r packagename.deb

to search for a package

aptitude search packagename

for example

aptitude search openssh

aptitude install packagename looks the /etc/apt/sources.list file and try to get the package from the resource specified there

aptitude remove packagename removes package

aptitude command take to interactive mode

search for package an + to mark it to be installed

press g to install