GNU/Linux Command – SHRED

shred — Overwrite/Delete a file securely.
 
Summary:
 
Overwrite the specified file repeatedly and remove, in order to make it harder to recover the data from HDD, using even a very expensive hardware probing tool.
 
Example:
$ shred file -- Repeatedly overwrite the file content with random data.  $ shred -v file -- Show progress info.  $ shred -n 5 file -- Overwrite 5 times (Default is 25).  $ shred -x file -- Use exact size. Don't round of.  $ shred -z file -- At the end of shred, overwrite the file with zeros.  $ shred -u file -- Overwrite, Truncate and Remove the file.
Read: man shred