Append N hexadecimal numbers to a binary file with Bash

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 $byte >> "output.bin" At some point I need to pad the file with a byte that could be anything from 00 to FF. I want to specify the byte as a hex value and the total of repetitions. I tried doing this with a for loop but it just takes too long, especially since I need to add something like 65535 bytes sometimes. byte="00" total=65515 for (( i=1; i> "output.bin" done I am looking for a more performant way that does not use a for loop. At the moment I am stuck with something between printf and echo but instead of writing the values as binary it writes them as text result=$(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 "x00". This is where I don't know how to proceed in order to make it write the actual binary value