Bash exit status when using while loop

Question

I have a bash script that goes through a list of ip's and pings them one by one. If the exit status for each ping is 0, then echo that the node is up, else the node is down.I am able to get this to work perfectly, but when the bash script ends the exit status is always 0.

What I am trying to achieve is for example out of 5 ip's if the 3rd one fails, to continue through the list and check the rest but once the script ends throw an exit status other than 0 and output which ip has failed.

cat list.txt |  while read -r output
do
    ping -o -c 3 -t 3000 "$output" > /dev/null
    if [ $? -eq 0 ]; then
    echo "node $output is up"
    else
    echo "node $output is down"
    fi
done

thanks in advance!

score 8 · Accepted Answer · edited Dec 02 '15 at 20:16

8

Your first problem is that by doing cat file | while read you've spawned the while in its own subshell. Any variables it sets will only exist during that loop, so persisting a value will be difficult. More info on that issue here.

If you use while read ... done < file it will work correctly. Make an exit status flag that defaults to zero, but set it to one if any errors occur. Use it as your script's exit value.

had_errors=0

while read -r output
do
    ping -o -c 3 -t 3000 "$output" > /dev/null
    if [ $? -eq 0 ]; then
        echo "node $output is up"
    else
        echo "node $output is down"
        had_errors=1
    fi
done < list.txt

exit $had_errors

edited Dec 02 '15 at 20:16

Siyual

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answered Dec 02 '15 at 15:54

Mr. Llama

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This looks to be doing what I was looking for. I was unaware of the first issue, and I understand. Thank you! – user2683183 Dec 02 '15 at 16:29
1

`cmd; if [ $? -eq 0 ]; then` is almost **always** better replaced with `if cmd; then`. – Etan Reisner Dec 02 '15 at 17:21

Bash exit status when using while loop

1 Answers1