how to empty recyclebin through command prompt?

You can effectively "empty" the Recycle Bin from the command line by permanently deleting the Recycle Bin directory on the drive that contains the system files. (In most cases, this will be the C: drive, but you shouldn't hardcode that value because it won't always be true. Instead, use the %systemdrive% environment variable.)

The reason that this tactic works is because each drive has a hidden, protected folder with the name $Recycle.bin, which is where the Recycle Bin actually stores the deleted files and folders. When this directory is deleted, Windows automatically creates a new directory.

So, to remove the directory, use the rd command (r​emove d​irectory) with the /s parameter, which indicates that all of the files and directories within the specified directory should be removed as well:

rd /s %systemdrive%\$Recycle.bin

Do note that this action will permanently delete all files and folders currently in the Recycle Bin from all user accounts. Additionally, you will (obviously) have to run the command from an elevated command prompt in order to have sufficient privileges to perform this action.

I prefer recycle.exe from Frank P. Westlake. It provides a nice before and after status. (I've been using Frank's various utilities for well over ten years..)

C:\> recycle.exe /E /FRecycle Bin: ALL    Recycle Bin C:  44 items, 42,613,970 bytes.    Recycle Bin D:   0 items, 0 bytes.            Total:  44 items, 42,613,970 bytes.Emptying Recycle Bin: ALL    Recycle Bin C:   0 items, 0 bytes.    Recycle Bin D:   0 items, 0 bytes.            Total:   0 items, 0 bytes.

It also has many more uses and options (output listed is from /?).

Recycle all files and folders in C:\TEMP:  RECYCLE C:\TEMP\*List all DOC files which were recycled from any directory on the C: drive:  RECYCLE /L C:\*.DOCRestore all DOC files which were recycled from any directory on the C: drive:  RECYCLE /U C:\*.DOCRestore C:\temp\junk.txt to C:\docs\resume.txt:  RECYCLE /U "C:\temp\junk.txt" "C:\docs\resume.txt"Rename in place C:\etc\config.cfg to C:\archive\config.2007.cfg:  RECYCLE /R "C:\etc\config.cfg" "C:\archive\config.2007.cfg"

nircmd lets you do that by typing

nircmd.exe emptybin

http://www.nirsoft.net/utils/nircmd-x64.zip
http://www.nirsoft.net/utils/nircmd.html