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About bash : In-Unix-shell-how-to-convert-from-hex-string-to-stdout-bytes-in-machine-endian-order

Question Detail

I’d like to run a command similar to:
# echo 00: 0123456789abcdef | xxd -r | od -tx1
0000000 01 23 45 67 89 ab cd ef

That is, I’d like to input a hex string and have it converted to bytes on stdout. However, I’d like it to respect byte order of the machine I’m on, which is little endian. Here’s the proof:
# lscpu | grep Byte.Order
Byte Order: Little Endian

So, I’d like it to work as above if my machine was big-endian. But since it isn’t, I’d like to see:
# | od -tx1
0000000 ef cd ab 89 67 45 23 01

Now, xxd has a “-e” option for little endianess. But 1) I want machine endianess, because I’d like something that works on big or little endian machines, and 2) “-e” isn’t support with “-r” anyway.

Question Answer

What about this —
$ echo 00: 0123456789abcdef | xxd -r | xxd -g 8 -e | xxd -r | od -tx1
0000000 ef cd ab 89 67 45 23 01

According to man xxd:

Switch to little-endian hexdump. This option treats byte groups as words in little-endian byte order. The default grouping of 4 bytes may be changed using -g. This option only applies to hexdump, leaving the ASCII (or EBCDIC) representation unchanged. The command line switches -r, -p, -i do not work with this mode.

-g bytes | -groupsize bytes
Separate the output of every bytes bytes (two hex characters or eight bit-digits each) by a whitespace. Specify -g 0 to suppress grouping. Bytes defaults to 2 in normal mode, 4 in little-endian mode and 1 in bits mode. Grouping does not apply to postscript or include style.

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