cat /dev/null > /var/mail/MAILBOX_YOU_WANT_TO_CLEAR

for example for user root you would use something like:

cat /dev/null > /var/mail/root

Top 20 Largest folders in a directory in Linux.

 du -shx * | sort -hr | head -n 20

Find All files larger than 50 megs in the entire system:

find / -type f -size +50M -exec ls -lh {} \; 2> /dev/null | awk '{ print $NF ": " $5 }' | sort -nrk 2,2

First

Create a Batch File “C:\myprogram.bat” with the following line in it (make sure you replace notepad with your own program):

runas /user:COMPUTERNAME\Administrator /savecred "C:\Program Files (x86)\Notepad++\notepad++.exe" 

Second

The first time you run the batch file above you will get prompted for your administrator password.

Run the Batch File first, so you can register your password.

Third

Disable the annoying DOS Prompt. Create another batch file and put the following lines in it:

Set WshShell = CreateObject("WScript.Shell" ) 
WshShell.Run chr(34) & "C:\myprogram.bat" & Chr(34), 0 
Set WshShell = Nothing 

Voila. You are good to go.