How to prepend 8 bytes of data to a binary file in Linux?

Question

I would like to add 8 bytes of data to the beginning of a binary file.

Is there a Linux command for this?

Answer 1

Here is one way to do that.

printf "\x68\x65\x6c\x6c\x6f\x20\x77\x6f" | cat - oldfile > newfile

The argument to printf is a sequence of 8 bytes in hex. Just replace the values I used (which are the ASCII characters "hello wo") with yours.

Answer 2

it is not 'the' command, it is 'a bunch of commands' (in good old unix tradition):

• put your 8 bytes to a file
• append the original file to that file
• rename the new file to the name of the original file.

or:

% echo -n "12345689" > new_file
% cat original >> new_file
% mv new_file original

or, if you need to read the 8 bytes from somewhere else:

% dd if=inputstream of=new_file bs=1 count=8

and then continue as above.