20

and vice versa.

I am running a RedHat if relevant.

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2
  • 6
    What type of binary file?
    – Stéphane Chazelas
    Commented Oct 29, 2015 at 16:47
  • 2
    In any case, for any file format, I'm sure you could write a one-liner to convert its endianness using Perl and pack / unpack. For some formats, it'll just be a longer line than for others. ;-)
    – Ilmari Karonen
    Commented Oct 29, 2015 at 21:13

4 Answers 4

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38

You can byteswap with dd. Is that sufficent? If not, please update your question to give an example of an input file and the expected outfile.

echo hello >infile
dd conv=swab <infile >outfile

hex infile
   0000 68 65 6c 6c 6f 0a                                 hello.
hex outfile
   0000 65 68 6c 6c 0a 6f                                 ehll.o
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35

You cannot do this because for such a conversion, you need to know the meaning of the binary content.

If e.g. there is a string inside a binary file it must not be converted and a 4 byte integer may need different treatment than a two byte integer.

In other words, for a byte order conversion, you need a data type description.

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  • 7
    I was just to say that. it is not as simple as just swapping every pair of bytes. for example a 4 byte integer 01 02 03 04 in bigendian could look like this in little endian 04 02 03 01 NOT 02 01 04 03 cs.umd.edu/class/sum2003/cmsc311/Notes/Data/endian.html
    – Rob
    Commented Oct 29, 2015 at 16:36
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    Agreed, endianness makes no sense on a raw, typeless byte stream... this should be the accepted answer if OP does not edit his question
    – Thomas
    Commented Oct 30, 2015 at 11:02
  • [citation needed] - AFAIK, unless an application explicitly preserves some byte order and not others, then it is usual for bytes or words to be consistently ordered throughout.
    – Dennis Williamson
    Commented Oct 30, 2015 at 15:52
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    @DennisWilliamson: A UTF-8 or ASCII string does not have endianness. UTF-8 specifies byte order while ASCII is 7 bit and doesn't have multi-byte tokens. A UTF-16 string does have endianness and may or may not have a BOM to mark that endianness. A Unix binary which is intended to interact with Windows or Java might have both types of string, which means you have to distinguish them when converting.
    – Kevin
    Commented Oct 30, 2015 at 18:42
  • I came here looking for a program where you give it the data description and the data and it converts it. Thus far I have not found such a program but that does not mean it cannot be done.
    – Levi Morrison
    Commented Aug 10, 2017 at 16:37
8

In order to change file endianess, assuming word (32-bit) size, this 1 liner should work for you:

hexdump -v -e '1/4 "%08x"' -e '"\n"' input_file | xxd -r -p > output_file
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1
  • Exactly what I needed when exploiting a str format vuln, The bytes came out in hex as 4 char reversed order (endianness).
    – Marshall Whittaker
    Commented Mar 20, 2021 at 2:54
2

If you don't care about file contents and just want to swap bytes, then try endconv. It is just a wrapper around standard byte conversion functions, so it supports conversion by 2, 4 and 8 byte long integers. It's not one liner though because it is separate program.

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