Using grep to search for hex strings in a file
I have been trying all day to get this to work. Does anyone know how to get grep, or something of the like, to retrieve offsets of hex strings in a file?
I have a bunch of hexdumps that I need to check for strings and then run again and check if the value has changed.
I have tried hexdump and dd, but the problem is because it's a stream, I lose my offset for the files.
Someone must have had this problem and a workaround. What can I do?
To clarify, I have a series of dumped memory regions from GDB.
I am trying to narrow down a number by searching out all the places the number is stored, then doing it again and checking if the new value is stored at the same memory location.
I cannot get grep to do anything because I am looking for hex values so all the times I have tried (like a bazillion, roughly) it will not give me the correct output.
The hex dumps are just complete binary files, the paterns are within float values at larges so 8? bytes?
The patterns are not wrapping the lines that I am aware of. I am aware of the what it changes to, and I can do the same process and compare the lists to see which match. The hex dumps normally end up (in total) 100 megs-ish.
Perl COULD be a option, but at this point, I would assume my lack of knowledge with bash and its tools is the main culprit.
Its a little hard to explain the output I am getting since I really am not getting any output..
I am anticipating (and expecting) something along the lines of:
<offset>:<searched value>
Which is the pretty well standard output I would normally get with grep -URbFo <searchterm> . > <output>
Problem is, when I try to search for hex values, I get the problem of if just not searching for the hex values, so if I search for 00 I should get like a million hits, because thats always the blankspace, but instead its searching for 00 as text, so in hex, 3030. Any idea's?
I CAN force it through hexdump or something of the link but because its a stream it will not give me the offsets and filename that it found a match in.
Using grep -b option doesnt seem to work either, I did try all the flags that seemed useful to my situation, and nothing worked.
Using xxd -u /usr/bin/xxd as an example I get a output that would be useful, but I cannot use that for searching..
0004760: 73CC 6446 161E 266A 3140 5E79 4D37 FDC6 s.dF..&j1@^yM7..
0004770: BF04 0E34 A44E 5BE7 229F 9EEF 5F4F DFFA ...4.N[."..._O..
0004780: FADE 0C01 0000 000C 0000 0000 0000 0000 ................
Nice output, just what I wana see, but it just doesnt work for me in this situation..
This is some of the things i've tried since posting this:
xxd -u /usr/bin/xxd | grep 'DF'
00017b0: 4010 8D05 0DFF FF0A 0300 53E3 0610 A003 @.........S.....
root# grep -ibH "df" /usr/bin/xxd
Binary file /usr/bin/xxd matches
xxd -u /usr/bin/xxd | grep -H 'DF'
(standard input):00017b0: 4010 8D05 0DFF FF0A 0300 53E3 0610 A003 @.........S.....
Answer
This seems to work for me:
LANG=C grep --only-matching --byte-offset --binary --text --perl-regexp "<\x-hex pattern>" <file>
short form:
LANG=C grep -obUaP "<\x-hex pattern>" <file>
Example:
LANG=C grep -obUaP "\x01\x02" /bin/grep
Output (cygwin binary):
153: <\x01\x02>
33210: <\x01\x02>
53453: <\x01\x02>
So you can grep this again to extract offsets. But don't forget to use binary mode again.
Note: LANG=C is needed to avoid utf8 encoding issues.