Editing Dd (Unix) (section)

=== In-place modification{{anchor|data modification}} ===
The command can modify data in place. For example, this overwrites the first 512 bytes of a file with null bytes:

<syntaxhighlight lang="bash">
dd if=/dev/zero of=path/to/file bs=512 count=1 conv=notrunc
</syntaxhighlight>

Option {{code|conv{{=}}notrunc}} requests to not truncate the output file. That is, if the output file already exists, replace the specified bytes and leave the rest of the output file as-is. Without this option, the command would create an output file 512 bytes long.