I have a Bash script that appends bytes written as hexadecimal values. I use echo to write the bytes and it works

hex="1F"
byte="\x$hex"
echo -en $byte >> "output.bin"

At some point I need to pad the file with a byte that could be anything from 00 to FF. I want to specify the byte as a hex value and the total of repetitions.

I tried doing this with a for loop but it just takes too long, especially since I need to add something like 65535 bytes sometimes.

byte="00"
total=65515
for (( i=1; i<=total; i++ ));
do
    echo -en "\x$byte" >> "output.bin"
done

I am looking for a more performant way that does not use a for loop. At the moment I am stack with something between printf and echo but instead of writing the values as binary it writes them as text

result=$(eval printf "\x$byte%0.s" {1..$total})
echo -en $result >> "output.bin"

The result in the output file is 78 30 30, which is the "x00" text, instead of 00. If I directly use echo -en "\x00" >> "output.bin", it does write one byte holding the 00 value and not the text "00". This is where I don't know how to proceed in order to make it write the actual binary value