linux script with netcat stops working after x hours

Question

I\'ve have to scripts:

#!/bin/bash

netcat -lk -p 12345 | while read line
do
    match=$(echo $line | grep -c \'Keep-Alive\')
    if [ $match -eq 1 ]; then
              


        

Answer 1

Periodically netcat will print, not a line, but a block of binary data. The read builtin will likely fail as a result.

I think you're using this program to verify that a remote host is still connected to port 12345 and 12346 and hasn't been rebooted.

My solution for you is to pipe the output of netcat to sed, then pipe that (much reduced) line to the read builtin...

#!/bin/bash

{
    echo "[$(date "+%F %T")] Starting loop."

    for (( ;; ))
    do
        echo "[$(date "+%F %T")] Starting netcat."

        netcat -lk -p 12345 | sed 's/.*Keep-Alive.*/Keep-Alive/g' | \
        \
        while read line
        do
            match=$(echo "$line" | grep -c 'Keep-Alive')
            if [ "$match" -eq 1 ]; then
                [start a command]
            fi
        done

        echo "[$(date "+%F %T")] Netcat has stopped or crashed."

        sleep 4s
    done
} >> "/var/log/something.log" 2>&1

Also, you'll need to review some of the other startup programs in /etc/init.d to make sure they are compatible with whatever version of rc the system uses, though, it would be much easier to call your script2.sh from a copy of some simple file in init.d. As it stands script2 is the startup script but doesn't conform to the init package you use.

That sounds more complicated that I mean... Let me explain better:

/etc/init.d/syslogd        ## a standard init script that calls syslogd
/etc/init.d/start-monitor   ## a copy of a standard init script that calls script2.sh

As an additional note, I think you could bind netcat to the specific IP that you are monitoring, instead of binding it to the all address 0.0.0.0