How can I run psql in the background and interact with it?

Using bash coproc is a smart option! It allows you to create a subprocess that you can communicate with easily. Here's a simple example using coproc:

```bash
coproc mycoproc { sed -u 's/function/coprocess/g' }

echo "Hello, function!" >&${mycoproc[1]}
read -r line <&${mycoproc[0]}
printf '%sn' "${line}"
kill "${mycoproc_PID}"
```
This way, you can keep the communication open without worrying about fd limitations!

Honestly, bash isn't the best choice for what you're trying to do. If you want something cleaner and more manageable, consider using Python or Perl. They can handle database interactions much more smoothly and give you more robust error handling. Save yourself the headache of dealing with file descriptors like this!

You definitely need a named pipe for this! When you start a background process, the parent and child have separate address spaces, so they can't see each other's stdin and stdout directly. However, be cautious when using named pipes in shell—you might run into performance issues if there's a lot of I/O. That said, if you're determined to use bash, you could try implementing a solution using bash coproc to manage your task instead. It'll handle everything without needing named pipes.