Linux Command - shred

shred - Overwrite file do destroy contents, optionally delete. This command will overwrite the file repeatedly making it very hard to recover even with expensive equipment.

NOTE - Be aware of mirrors and backups.

shred file1.txt
shred -n 100 file1.txt
shred -u file1.txt
shred -z file1.txt

-f	force, change perms to allow writing if needed
-n	interations ( default is 3 )
–random-source=FILE	use this as a random source
-s	shred this many bytes
-u	deallocate and remove file after overwriting
–remove	same as -u but specify how ( unlink, wipe, wipesync )
-v	verbose, show progress
-x	exact, do not round file sizes up
-z	add a final overwrite with zeros to hide shredding
-u / –remove	might not make sense with a device ( ex: /dev/sda )