BASH: Read lines from netcat connection

Question

I have a simple script which reads some lines from a connection initialized using netcat. A client can transmit some "commands". If the client write "exit" I like to close the connection.

BUT: After transmit the "exit" the script echos the "Received 'exit'" but still reads one more line before the "Good bye" appears.

echo "Start listening on port $PORT ..."
    (echo "Welcome. Please give me one of the following commands: 
            $AVAILABLECOMMANDS") | nc -q -1 -l $PORT | while read line
    do
            if [ "$line" == 'exit' ]; then
                    echo "Received 'exit'"
                    break
            else
                    result=$(executeCommand $line)
                    echo "$result"
            fi
    done
    echo "Good bye"

I think I have to rewrite the loop but I have no idea how.

Can somebody help?

Thank you.

Answer 1

As explained here, bash made the choice to exit only when all the commands in the pipe as ended. Here, netcat does not want to stop, but after since the end pipe is broken, netcat fails. That's why you need to wait one more time to quit the loop (by the way, you have an error when you quit the loop). Here is a version that doesn't have this pipe problem :

#!/bin/bash

echo "Start listening on port 12345 ..."
while read line
do
    if [ "$line" == 'exit' ]; then
        echo "Received 'exit'"
        break
    else
        echo "$line"
    fi
done < <((echo "Welcome. Please give me one of the following commands: $AVAILABLECOMMANDS") | nc -q -1 -l 12345)
echo "Good bye"

Answer 2

Handy way to get incoming data and transmit data over netcat.

#!/bin/bash

netcat -l localhost 12345  # port 12345
exec 6<>/dev/tcp/localhost/12345

while read <&6
do
        echo "$REPLY"
done