Unix 在模式匹配之前，如何阻塞管道？

我如何才能阻塞管道，直到模式匹配为止？ 我想这样做：

#!/bin/sh

mkfifo request response
while true; do # needs to send one response at a time
  nc -N -l 127.0.0.1 4000 >request <response & # send output to request pipe
  sed -u '/^$/q' <request; # block until a blank line is received
  date | tee response # send input back to the original command
done

#/垃圾箱/垃圾箱
mkfifo请求响应
虽然真实；是否需要一次发送一个响应
nc-N-l 127.0.0.1 4000>请求如果与模式匹配的操作被阻塞，则可以使用cat防止数据从命名管道中流出，直到有东西写入到命名管道中。cat将从指定管道读取数据，直到写入EOF

#!/bin/sh

mkfifo response
while true; do # send one response at a time
  cat response | nc -N -l 127.0.0.1 4000 | # pipe request out
  (
    sed -u '/^$/q' # block until a blank line is received
    date | tee response # send input back to the original command
  )
done