Bash script behaves unexpected / Strange

Question

First I want to apologize for being an absolute noob at programming, writing scripts, etc. I'm running a FreeNAS Server and a Raspberry Pi which I'd like to include a sh-Script which should check if 8 clients (IP addresses) are online. If yes they should stop but if all IP's are offline, it should perform another task / script.

Here's my problem: On the internet (src: https://www.tech-blogger.net/freenas-automatisch-bei-nicht-benutzung-abschalten/) I found a script which checks specific IP's and if they're offline it should shutdown automatically. When I ping those addresses I get 100% package lost which indicates that they are offline. But the script echos me that at least one client is offline. Because I'm not THAT dumb I assume that it has something to do with my code. Does anyone know what goes wrong with my Script?:

HOST1=192.168.1.32
HOST2=192.168.1.33
HOST3=192.168.1.34
HOST4=192.168.1.35
HOST5=192.168.1.36

_exit () {
case $1 in
1) echo „No Shutdown – At least one PC is online“ ;;
2) echo „No PC is online – Shutdown“ ; shutdown -p now ;;
esac
exit $1;
}

#Check if IPs are online
if [ `ping -c 1 -i 1 $HOST1 | grep -wc 100.0%` -eq 0 ] || [ `ping -c 1 -i 1 $HOST2 | grep -wc 100.0%` -eq 0 ] || [ `ping -c 1 -i 1 $HOST3 | grep -wc 100.0%` -eq 0 ] || [ `ping -c 1 -i 1 $HOST4 | grep -wc 100.0%` -eq 0 ] || [ `ping -c 1 -i 1 $HOST5 | grep -wc 100.0%` -eq 0 ] ; then _exit 1;

#All Clients are offline, shutdown
else
_exit 2
fi
fi

if [ $(cmd | grep -c ...) -eq 0 ] is an anti-pattern. Use if ! cmd | grep -q ... instead — William Pursell
– William Pursell, Commented May 27, 2019 at 17:08
But you shouldn't be using grep at all here. ping will return 0 if it receives a response, non-zero otherwise, so you can just do if ( ping -c 1 -t 1 $HOST1 || ping -c 1 -t 1 $HOST2 || ... ) > /dev/null 2>&1 ; then to see if any host responds. — William Pursell
– William Pursell, Commented May 27, 2019 at 17:21

Community · Accepted Answer · 2020-06-20 09:12:55Z

0

I am not 100 % sure if I get your Problem right. But I think you should try to replace || with && in your if statement.

|| = or && = and

Thus it will only go into the shutdown parts, when all Clients are off.

edit:

ping -c 1 -i 1 192.168.1.36
PING 192.168.1.36 (192.168.1.36) 56(84) bytes of data.
From 62.155.241.85 icmp_seq=1 Destination Host Unreachable

--- 192.168.1.36 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms

It's 100% packet loss not 100.0%. Thus you check for something that does not occur.

#!/bin/bash

HOST1=192.168.1.32
HOST2=192.168.1.33
HOST3=192.168.1.34
HOST4=192.168.1.35
HOST5=192.168.1.36

_exit () {
case $1 in
1) echo „No Shutdown – At least one PC is online“ ;;
2) echo „No PC is online – Shutdown“ ;; # shutdown -p now ;;
esac
exit $1;
}

#Check if IPs are online
if [ `ping -c 1 -i 1 $HOST1 | grep -wc 100%` -eq 0 ] || [ `ping -c 1 -i 1 $HOST2 | grep -wc 100%` -eq 0 ] || [ `ping -c 1 -i 1 $HOST3 | grep -wc 100%` -eq 0 ] || [ `ping -c 1 -i 1 $HOST4 | grep -wc 100%` -eq 0 ] || [ `ping -c 1 -i 1 $HOST5 | grep -wc 100%` -eq 0 ] ; then _exit 1;

#All Clients are offline, shutdown
else                                                                                                                                                                                           
_exit 2
fi

This works as expected ( on my machine ). :-)

edited Jun 20, 2020 at 9:12

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answered May 27, 2019 at 14:13

rblock

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1 Comment

AlphaInc. Over a year ago

Yes this worked fine. Thank you very much for your help :-)

Dennis Williamson · Accepted Answer · 2019-05-27 19:25:13Z

0

As William Pursell said in a comment, when ping doesn't reach the requested IP, it returns a non-zero exit code indicating failure. The if statement in shells like Bash can use that exit code directly without having to use bracketed conditional expressions.

I would recommend a loop instead of a long conditional. This will be easier to read and maintain and scales more readily if the number of hosts change.

# create an array of IPs
host_ips=(
    192.168.1.32
    192.168.1.33
    192.168.1.34
    192.168.1.35
    192.168.1.36
)

for ip in "${host_ips[@]}"
do
    if ping -c 1 -i 1 "$ip"
    then
        _exit 1
        # no need to break since _exit doesn't return
    fi
done
# if we made it this far, none are online
_exit 2

answered May 27, 2019 at 19:25

Dennis Williamson

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2 Comments

AlphaInc. Over a year ago

I tried this but my Raspberry tells me there is a syntax error because of the ( in the second line.

Dennis Williamson Over a year ago

@AlphaInc.: You need to make sure you're using Bash and not sh since the former supports arrays and the latter usually doesn't. #!/bin/bash should be the first line in your script.

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