To scan for WiFi networks, use the command
pi@raspberrypi: ~$ sudo iwlist wlan0 scan|grep "ESSID"
example output:
ESSID:"darkroom"
ESSID:"mynetwork"
ESSID:"bluetuna"

Dosbox keyboard messed up?
Happens when running Dosbox from a Pi started in CLI
$ sudo nano /home/pi/.dosbox/dosbox-0.74.conf
     usescancodes=false

Install software
If you're not sure what you're looking for or just wish to browse through what's available, you can alternatively use the menu-driven tool Aptitude:
$ sudo aptitude

Then use apt-cache to search for the package that you want to install, in this case,
$ apt-cache search APPNAME
You can pipe the output to a text file for later reading
$ apt-cache search APPNAME > test.txt

Remove unwanted programs
$ sudo apt-get --purge remove APPNAME
   (minecraft-pi, claws-mail)
     or run aptitude by itself

If your Raspberry Pi just seems realy flakey.
Get a bigger power supply!

You think the SD card is corrupt? You would like to do a "Chkdisk"?
Force  the system to check the volumes on boot up
$ sudo touch /forcefsck
Then reboot
(better!! add "
touch /forcefsck" to /etc/rc.local (before "exit 0")
     to check file system at every boot!)

Network Wha???
Route                View IP route table 
iwconfig            View Wireless devices
ifconfig              View IP info of all interfaces


Using Google Chrome with Secure SSH to access the Pi
and you see this....

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@                                                  @
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@                                                  @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

in Google Chrome - "Ctrl+Shift+J"
make sure "Console" is highlighted on the menu bar, paste the following and try again
term_.command.removeAllKnownHosts();


I thought I saw something during boot up
~ $ dmesg        (view the boot logs, scroll back if needed)

I see a prompt - but where am i in the directory tree?
$ pwd              Print Working Directory
$ arch             Display hardware architecture
$ sudo nano filename   edit text file on the screen
$ ls               List files
$ cd directory     Change to directory
$ cd ..            Change directory up(back) one level
$ mkdir directory  Make directory
$ clear            clear screen
$ more filename    display text file on the screen
$ head filename   \
      
or       display the first or last 10 lines of a file
$ tail filename   /
$
sudo mv filename directory
     move a file to a different directory
$ cp filename newfile   new copy (duplicate a file)
$ rm filename     remove (delete) filename (might need sudo)
$ touch filename Create filename
$ man command     an interface to the on-line reference manuals
                        (
try $ man man )
$ alias           used to set up alternative names for commands
                         $ alias up='cd ..'
$
Help           for a command list

If it seems an installation is missing stuff,
 
append      --fix-missing     to the apt-get command
$ sudo apt-get install xbmc --fix-missing

Been adding & removing left & right?
Probably have snippets and parts of apps here and there?
Remove dead unconnected packages..
$ sudo apt-get autoremove

What kind of CPU do I have?
$ cat /proc/cpuinfo
$ cat /proc/meminfo    displays details about the Raspberry Piís memory
$ cat /proc/partitions reveals the partitions on your SD card or HDD
$ cat /proc/version    shows you which version of the Pi you are using.

$ vcgencmd measure_temp  CPU temperature
$ vcgencmd commands      for the list

If you get message during an installation similar to
  Failed to fetch http://mirrordirector.raspbian.org/
Check the file /etc/resolv.conf
and make sure you have an entry to an outside DNS provider like google
nameserver 8.8.8.8