binary file editing using python script

Question

I want to do some operation on binary file using python script. I have one binary file. And I want to append binary data to it.

Example:
File abc.bin is available.

Command:

python file_append.py abc.bin 1234 5678

I want to append "1234" and "5678" at the end of the binary file abc.bin.

So I opened the file with "ab" mode (append + binary). When I append a command line argument, it appends the ASCII value of the argument.

How can I append the hex value (here 1234 and 5678) at the end of the file?

Code:

fo = open(str(sys.argv[1]), 'ab')
fv = string.atoi(sys.argv[2])
ft = string.atoi(sys.argv[3])
fo.write(fv)

so you want to append 4 bytes with hexa values 12, 34, 56, and 78? — ewcz
– ewcz, Commented Sep 26, 2015 at 9:29

ewcz · Accepted Answer · 2015-09-26 09:55:51Z

1

if you want to parse the command line arguments, split them into two-digit groups, interpret then these numbers as ASCII hexa codes and append this at the end of the binary file of interest, then you could do something like this

of = open(sys.argv[1], 'ab')
for arg in sys.argv[2:]:
    val = int(arg)
    for b in (val/100, val%100):
        of.write(chr(int(str(b), base=16)))

python file_append.py abc.bin 1234 5678 then produces file abc.bin the content of which can be checked with hexdump -C abc.bin which shows

00000000  12 34 56 78                                       |.4Vx|
00000004

answered Sep 26, 2015 at 9:55

ewcz

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4 Comments

PM 2Ring Over a year ago

This won't cope with data containing hex digits > 9.

ewcz Over a year ago

that it won't, I was assuming (perhaps mistakenly) that the input is expected to be a decimal integer...

PM 2Ring Over a year ago

Fair enough. But in that case, your code is still wrong, because it interprets '1234' as 0x1234 instead of 0x04d2.

ewcz Over a year ago

as far as I can tell, it gives the same output as the approach using a2b_hex so it seems that it does what was desired (for input containing only decimal digits)...

PM 2Ring · Accepted Answer · 2015-09-26 11:34:42Z

0

I solved it with the code below.

fo = open(str(sys.argv[1]), 'ab')
f1 = binascii.a2b_hex(sys.argv[2])
fo.write(f1)
f2 = binascii.a2b_hex(sys.argv[3])
fo.write(f2)
fo.close()

Thanks for your response.

edited Sep 26, 2015 at 11:34

PM 2Ring

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answered Sep 26, 2015 at 10:13

Dhaval Chauhan

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1 Comment

PM 2Ring Over a year ago

You could join the data strings into one string & pass that to a2b_hex, rather than converting & writing each separately. And then your program could cope with any number of data strings. Eg, binascii.a2b_hex(''.join(sys.argv[2:]))

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