While you can use the dd command to overwrite your files, you can also use shred. Shred by default will overwrite your files 3 times and is designed to make it very hard to recover those files. There are several options you can use such as how many times you wish to overwrite the specified file or files, how many bytes, etc. Here are the available options below.
In this guide I will be showing you how to wipe your hard drives using the dd command. You have a few options when it comes to wiping your hard drives, you can wipe the MBR (master boot record) or you can wipe the entire drive. If you are looking for a guide on wiping specific files only, then please read about the shred command.