well, why is the file going blank if i use > even though the file exists and has contents

Because that is what > means, see open

you can understand in this way:
The file name here is where you save your work. 
( you use close() to save your file )
So it doesn't matter the file has data inside or not. 
ONLY the data in the handle will write to your file.
ie. This ">" is an overwrite, if you are opening an existed file

So, since you are open a file for WRITE, so it couldn't READ, while you read
nothing, so you write nothing. End up, you harvest an empty file

ok i got it, i just wanted to know any way i can open already existing file change it on the fly

">" and ">>" are pipelines.

For Perl and bash (one of the linux shells) ">" is the standard way to say: "redirect this stuff to the named file and overwrite (delete) its previous contents with this".

And ">>" is the standard way to say: "add this material after the last line of the file (updating this contents) but preserve any previous contents that you found in this file". ">>" works also in perl and in bash

If the file is missing both do basically the same. Create a "box" (the file) and dump all the "bricks" into this box.

So, let's see what are you doing:

 open (HAN , ">" ,'D:\RAM\perl\test') or die "$!"; 
# DELETE the contents of this file and open it
while (<HAN>){
 s/e/\*\*/ig; 
# nothing here to mach, the file is empty, no survivor "e" chars
 print HAN ; 
# thus, nothing is changed and nothing left to print to the file
}
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