Introduction
Earlier in the year I wrote a Lua implementation of xxd -i (it’s at the bottom under the “Embedding” section). I wrote this because a few platforms I was working with didn’t support xxd. I didn’t want to attempt compiling and installing it. I had Lua installed on these platforms so it was easier to write a Lua script to do the same thing. I only needed -i output so implementing all of xxd wasn’t necessary. Plus it was fun.
Since then I’ve run into another issue with xxd -i. Specifically, I have a generated header and I don’t have the original file it was created from. In this case it’s a PNG. xxd supports a -r option for reversing its output. However, it doesn’t support reversing files generated with the -i option…
Solution
I wrote a script to reverse xxd -i output and turn it back into the original file. This time I used Python and not Lua. Python made it easier and I didn’t need to run it on the platforms that didn’t support xxd (or Python). I really should have implementations in both Languages; that might be a future project.
Here is the Python file for reversing the xxd -i output. I’ve also put both scripts on GitHub as Bin-Header.
header2bin.py
#!/usr/bin/env python
# The MIT License (MIT)
#
# Copyright (c) 2015 John Schember <john@nachtimwald.com>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
import re
import struct
import sys
'''
Output a binary file that was created with xxd -i.
xxd cannot reverse its output when using the -i
(C header file output).
'''
def main(args):
# Check arguments
if '-h' in args or '--help' in args:
print('Usage: %s infile outfile' % args[0])
print('Reverse a C header generated by xxd -i back to a binary file.')
return 1
if len(args) != 3:
print('%s invalid option' % args[0])
print('Try '%s --help' for more information.' % args[0])
return 2
# Setup our variables
infile = args[1]
outfile = args[2]
indata = ''
hexnums = []
# Read the file
try:
with open(infile, 'rb') as f:
indata = f.read()
except Exception as e:
print('Failed to read '%s': %s' % (infile, e))
return 3
# Prepare the file
# Remove all newlines from the file so we can match as if it was one string
indata = re.sub('[rn]+', '', indata)
# Match the start and end pulling out the part with the hex numbers
match = re.match('^unsigned char.*[].*=.*{(.*)};.*unsigned int.*$', indata)
if not match:
print('File does not have proper format')
return 3
# Be safe that we actually captured the hex numbers
try:
indata = match.group(1)
except Exception as e:
print('Hex data group not found')
return 3
# Pull out the hex numbers. We do this instead of a split
# so we don't have to worry about any other formatting.
pat = re.compile('0x[0-9a-fA-F]{2}')
for h in re.findall(pat, indata):
hexnums.append(h)
# Be sure we found some data
if len(hexnums) == 0:
print('Could not find any hex number data')
return 3
# Write the numbers as binary to the output file
try:
with open(outfile, 'wb') as f:
for h in hexnums:
# Pack it into binary. xxd by default outputs as big endian.
# There is an option in some implementations (-e) that will
# output as little endian. This doesn't matter because we're
# writing single bytes.
f.write(struct.pack('B', int(h, 16)))
except Exception as e:
print('Failed to write '%s': %s' % (outfile, e))
return 3
return 0;
if __name__ == '__main__':
sys.exit(main(sys.argv))