SC3032

#!/bin/sh
coproc nc shellcheck.net 80

Either switch to Bash:

#!/usr/bin/env bash
coproc nc shellcheck.net 80

or try to write your script in a POSIX compatible way using named pipes.

Your script uses a shell feature not supported by the shebang. Either rewrite the script to be portable, or change the shebang to explicitly require a shell like Bash.

There is no simple substitution for a coproc, though many use cases can be rewritten via redirection to named pipes (mkfifo).

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