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.

link|improve this question
feedback

2 Answers

up vote 3 down vote accepted

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

link|improve this answer
feedback

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

link|improve this answer
How do you prevent it from changing the actual data of inputFile.bin? – Daniel Beck Apr 25 '11 at 6:28
I don't know, just found that command by googling for /dev/zero opposite :) – kev Apr 25 '11 at 6:36
Well, it converts zeros to ones, but not only in the padding area. He doesn't end up with a lot of the data from inputFile.bin, does he? – Daniel Beck Apr 25 '11 at 6:38
Right, didnt read the question very well. – kev Apr 25 '11 at 6:41
feedback

Your Answer

 
or
required, but never shown

Not the answer you're looking for? Browse other questions tagged or ask your own question.