Hexdump reverse command

Question

The hexdump command converts any file to hex values.

But what if I have hex values and I want to reverse the process, is this possible?

Answer 1

I've written a short AWK script which reverses hexdump -C output back to the original data. Use like this:

reverse-hexdump.sh hex.txt > data

Handles '*' repeat markers and generating original data even if binary. hexdump -C and reverse-hexdump.sh make a data round-trip pair. It is available here:

• GitHub reverse-hexdump repo
• Direct to reverse-hexdump.sh

Answer 2

There is a similar tool called xxd. If you run xxd with just a file name it dumps the data in a fairly standard hex dump format:

# xxd bdata
0000000: 0001 0203 0405
......

Now if you pipe the output back to xxd with the -r option and redirect that to a new file, you can convert the hex dump back to binary:

# xxd bdata | xxd -r >bdata2
# cmp bdata bdata2
# xxd bdata2
0000000: 0001 0203 0405

Answer 3

If you have only a hexdump generated with hexdump you can use the following command

sed -E 's/ /: /;s/ (..)(..)/ \2\1/g;$d' dump | xxd -r

The sed part converts hexdump's format into xxd's format, at least so far that xxd -r works.

Known Bugs (see comment section)

• A trailing null byte is added if the original file was of odd length (e.g. 1, 3, 5, 7, ..., byte long).
• Repeating sections of the original file are not restored correctly if they were hexdumped using a *.

Answer 4

There is a tonne of more elegant ways to get this done, but I've quickly hacked something together that Works for Me (tm) when regenerating a binary file from a hex dump generated by hexdump -C some_file.bin:

sed 's/\(.\{8\}\)  \(..\) \(..\) \(..\) \(..\) \(..\) \(..\) \(..\) \(..\)/\1: \2\3 \4\5 \6\7 \8\9/g' some_file.hexdump | sed 's/\(.*\)  \(..\) \(..\) \(..\) \(..\) \(..\) \(..\) \(..\) \(..\)  |/\1 \2\3 \4\5 \6\7 \8\9  /g' | sed 's/.$//g' | xxd -r > some_file.restored

Basically, uses 2 sed processeses, each handling it's part of each line. Ugly, but someone might find it useful.