Answer by Dennis Williamson for How do I print an ASCII character by different code points in Bash?

Decimal:

chr() {
    local c
    for c
    do
        printf "\\$((c/64*100+c%64/8*10+c%8))"
    done
}

chr 74

Hex:

chr $((16#4a))

The function can do sequences:

$ chr 74 75 76; echo
JKL
$