Using grep to search for hex strings in a file_问答_开发者

Does anyone know how to get grep, or similar tool, to retrieve offsets of hex strings in a file?

I have a bunch of hexdumps (from GDB) 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 (typically several hundred MB)
I am trying to narrow down a number by searching for 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 line-wrapping, as far as I am aware. I am aware of the what it changes to, and I can do the same process and compare the lists to see which match.

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.

Desired output format

It's 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 we开发者_如何学运维ll standard output I would normally get with grep -URbFo <searchterm> . > <output>

What I tried:

A. 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?

B. 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.

C. Using grep -b option doesnt seem to work either, I did try all the flags that seemed useful to my situation, and nothing worked.

D. 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 want to see, but it just doesn't work for me in this situation..

E. Here are 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.....

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.

There's also a pretty handy tool called binwalk, written in python, which provides for binary pattern matching (and quite a lot more besides). Here's how you would search for a binary string, which outputs the offset in decimal and hex (from the docs):

$ binwalk -R "\x00\x01\x02\x03\x04" firmware.bin
DECIMAL     HEX         DESCRIPTION
--------------------------------------------------------------------------
377654      0x5C336     Raw string signature

We tried several things before arriving at an acceptable solution:

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.....

Then found we could get usable results with

xxd -u /usr/bin/xxd > /tmp/xxd.hex ; grep -H 'DF' /tmp/xxd

Note that using a simple search target like 'DF' will incorrectly match characters that span across byte boundaries, i.e.

xxd -u /usr/bin/xxd | grep 'DF'
00017b0: 4010 8D05 0DFF FF0A 0300 53E3 0610 A003  @.........S.....
--------------------^^

So we use an ORed regexp to search for ' DF' OR 'DF ' (the searchTarget preceded or followed by a space char).

The final result seems to be

xxd -u -ps -c 10000000000 DumpFile > DumpFile.hex
egrep ' DF|DF ' Dumpfile.hex

0001020: 0089 0424 8D95 D8F5 FFFF 89F0 E8DF F6FF  ...$............
-----------------------------------------^^
0001220: 0C24 E871 0B00 0083 F8FF 89C3 0F84 DF03  .$.q............
--------------------------------------------^^

grep has a -P switch allowing to use perl regexp syntax the perl regex allows to look at bytes, using \x.. syntax.

so you can look for a given hex string in a file with: grep -aP "\xdf"

but the outpt won't be very useful; indeed better do a regexp on the hexdump output;

The grep -P can be useful however to just find files matrching a given binary pattern. Or to do a binary query of a pattern that actually happens in text (see for example How to regexp CJK ideographs (in utf-8) )

I just used this:

grep -c $'\x0c' filename

To search for and count a page control character in the file..

So to include an offset in the output:

grep -b -o $'\x0c' filename | less

I am just piping the result to less because the character I am greping for does not print well and the less displays the results cleanly. Output example: