How to pad a file with “FF” using dd?

Question

How to pad a file with 0xFF using dd?

This command will pad the output file with zeroes until the file size reaches 100 KB:

dd if=inputFile.bin ibs=1k count=100 of=paddedFile.bin conv=sync

However, I want to pad a file with 0xFFs instead of 0x00s.

Answer 1

You can first create paddedFile.bin filled with 0xFF. Then insert the content of inputFile.bin.

$ tr "\000" "\377" < /dev/zero | dd ibs=1k count=100 of=paddedFile.bin
100+0 records in
200+0 records out
102400 bytes (102 kB) copied, 0,0114595 s, 8,9 MB/s
$ hexdump -C paddedFile.bin 
00000000  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
*
00019000
$ hexdump -C inputFile.bin 
00000000  66 6f 6f 0a 62 61 72 0a                           |foo.bar.|
00000008
$ dd if=inputFile.bin of=paddedFile.bin conv=notrunc
0+1 records in
0+1 records out
8 bytes (8 B) copied, 7,4311e-05 s, 108 kB/s
$ hexdump -C paddedFile.bin 
00000000  66 6f 6f 0a 62 61 72 0a  ff ff ff ff ff ff ff ff  |foo.bar.........|
00000010  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
*
00019000

In the second dd invocation you have to use conv=notrunc so the output file does not get truncated.

Credits go to @kev (and this commandlinefu.com article) for the trick using tr to convert 0x00 to 0xFF

Answer 2

i found a solution on comandlinefu, it involves tr to change the zeros to ones.

http://www.commandlinefu.com/commands/view/6483/fill-a-hard-drive-with-ones-like-zero-fill-but-the-opposite-

Good Luck