bash get fd with temporary file in memory linked

fd_w_f.sh

#!/bin/bash

get_fd() {
    local x
    local tmpfile
    local _fd_var=$1
    
    for x in $(seq 10 $(ulimit -n)); do
        if [[ ! -a "/proc/$BASHPID/fd/$x" ]]; then
            tmpfile=$(mktemp /dev/shm/XXX.tmp)
            exec {x}<>$tmpfile 
            printf -v "$_fd_var" %s "$x"
            rm $tmpfile
            return
        fi
    done
    echo 0
}


get_fd tf_fd

echo hello >&$tf_fd
cat /dev/fd/$tf_fd