Linux: Delete all contents of file by only a command in vi editor

To clear the contents of a file is opening. Let's try folow the following command.

           :1,$d

Other basic useful command :
* Create a file
vi filename
* To exit vi and save changes:
         ZZ   or  :wq
* To exit vi without saving changes:
         :q!
* To edit file content :
         i
* Deleting Text :

*	x	delete single character under cursor
	Nx	delete N characters, starting with character under cursor
	dw	delete the single word beginning with character under cursor
	dNw	delete N words beginning with character under cursor;   e.g., d5w deletes 5 words
	D	delete the remainder of the line, starting with current cursor position
*	dd	delete entire current line
	Ndd or dNd	delete N lines, beginning with the current line;   e.g., 5dd deletes 5 lines

* Searching Text:

	/string	search forward for occurrence of string in text
	?string	search backward for occurrence of string in text
	n	move to next occurrence of search string
	N	move to next occurrence of search string in opposite direction

* Screen Manipulation:

	^f	move forward one screen
	^b	move backward one screen
	^d	move down (forward) one half screen
	^u	move up (back) one half screen
	^l	redraws the screen
	^r	redraws the screen, removing deleted lines