理解bash exec{logout}？

下面的Bash命令做什么

exec {logout}> >(tee -a "${LOGFILE}")

或

---

从Bash参考资料中，关于：

每个重定向之前可能有一个文件描述符编号，但之前可能有一个

{varname}

形式的单词。在这种情况下，除了

&-

和

exec {logout}>> "${LOGFILE}"

exec {logout}> >(tee -a "${LOGFILE}")

tee -a "${LOGFILE}"

#!/bin/bash

logfile=testlogfile

exec {logout}> >(tee -a "$logfile")
echo "logout=$logout"

# now output some stuff to fd $logout:
echo >&"$logout" "Hello file descriptor $logout"

# it will send the message to tee, so that you'll see it on stdout
# and will also be appended to $logfile

# Check that output really got to $logfile:
cat "$logfile"

exec {logout}>&-

ls /dev/fd