Question

I want to run the command:

nc localhost 9998

Then I want my script to monitor a file and echo the contents of the file to this sub process whenever the file changes.

I can’t work out the re-direction scheme. How can get access to the STDIN of the subprocess?

Answer 1

Two solutions that I found acceptable:

1) use coprocess, this way we have access to stdin and stdout of the process created by the coprocess command via the COPROC[0/1] array.

2) What I ultimately did is separate my application into two code blocks as shown below. The first block writes to stdout, that is then piped to the stdin of the second block. This gives me a clean way to buffer data when there are issues with netcat in the second code block:

{ while true;
  write to STDOUT; } |
{ while true
  nc localhost 9998 }

(in actuality the script is far more complex as the second command provides to-disk buffering when netcat is unable to connect, but the use of the pipe provides buffering so that data isn’t lost when a network issue interrupts netcat)