Re: How to keep tcp connection open?

[Koichi Murase]

2024年5月13日(月) 23:28 Peng Yu <pengyu.ut@gmail.com>:
> If I just run the following command in an interactive session,
>
> read -N 4 var < /dev/tcp/127.0.0.1/2828

A redirection for a normal command is closed at the command's
termination. You need to open a file descriptor using `exec
<redirection>'.
  $ exec {fd1}< /dev/tcp/127.0.0.1/2828

Then, you can read from the file descriptor using
  $ read -N 4 -u "$fd1" var
or
  $ read -N 4 var <&"$fd1"

You can continue to use the file descriptor.

> read -N "$((n-${#n}))" rest < /dev/tcp/127.0.0.1/2828

$ read -N "$((n-${#n}))" rest <&"$fd1"

However, it should be noted that if it takes time to input the next
command, the connection might be closed by the remote end for a
timeout.

After finishing the transaction, you can close the file descriptor by

$ exec {fd1}>&-

--
Koichi