Bash的读/写文件的描述 - 寻求启动文件

我试图用读/写文件描述符在bash，这样我可以删除该文件描述提到这个文件后来，因为这样的：

I tried to use the read/write file descriptor in bash so that I could delete the file that the file descriptor referred to afterward, as such:

F=$(mktemp)
exec 3<> "$F"
rm -f "$F"

echo "Hello world" >&3
cat <&3

但猫命令不会有任何输出。我能达到我想要的，如果我使用单独的文件描述符进行读取和写入：

but the cat command gives no output. I can achieve what I want if I use separate file descriptors for reading and writing:

F=$(mktemp)
exec 3> "$F"
exec 4< "$F"
rm -f "$F"

echo "Hello world" >&3
cat <&4

这版画世界，你好。

我怀疑的bash当你从写转换到读它，而下面的bash和python code组合证实了这一点并不会自动寻求文件描述符的启动：

I suspected that bash doesn't automatically seek to the start of the file descriptor when you switch from writing to reading it, and the following combination of bash and python code confirms this:

fdrw.sh

exec 3<> tmp
rm tmp

echo "Hello world" >&3
exec python fdrw.py

fdrw.py

fdrw.py

import os  

f = os.fdopen(3)
print f.tell()
print f.read()

这给：

$ bash fdrw.sh
12

$ # This is the prompt reappearing

有没有一种方法可以达到我只想使用bash是什么？

Is there a way to achieve what I want just using bash?