Writing hex values to a file (not as ascii values) via the command line

command-line-interfacehexidecimal

I was wondering if anybody knew of a command line utility that would allow me to directly write hex values to a file. such that when a hexdump of the file is done the values that I enter would be spit out. It is vital that I write directly to hex as many of the value that I need to write do not have any unicode or ascii equivalent characters associated with them.
Looking for something like:

writehex f6050000 ac7e0500 02000800 01000000 newfile
hexdump newfile 
hexdump 1.02
ts.event.1
00000000: f6050000 ac7e0500 02000800 01000000 .....~..........
16 bytes read

Best Answer

This Bash function should work for you:

writehex  ()
{
    local i
    while [ "$1" ]; do
        for ((i=0; i<${#1}; i+=2))
        do
            printf "\x${1:i:2}";
        done;
        shift;
    done
}

Alternative implementation:

writehex  ()
{
    local arg, i
    for arg; do
        for ((i=0; i<${#arg}; i+=2))
        do
            printf "\x${arg:i:2}"
        done
    done
}

To test it:

$ writehex abc00001ff | hexdump -C
00000000  ab c0 00 01 ff                                    |.....|
00000005

$ writehex f6050000 ac7e0500 02000800 01000000 | hexdump -C
00000000  f6 05 00 00 ac 7e 05 00  02 00 08 00 01 00 00 00  |.....~..........|
00000010

Another option would be to use xxd.

$ echo hello | xxd
0000000: 6865 6c6c 6f0a
$ echo hello | xxd | xxd -r
hello

Edit:

Additionally, you can use the -p option to accept somewhat freeform input data:

$ echo 'f6050000 ac7e0500 02000800 01000000' | xxd -r -p | hexdump -C
00000000  f6 05 00 00 ac 7e 05 00  02 00 08 00 01 00 00 00  |.....~..........|
00000010

Edit 2:

Modified function above to handle multiple input arguments (strings of hex digits separated by spaces).

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