Bash loop ping successful

Question

I'm thinking that this needs to be changed to a while clause, at the moment it'll wait till all 10000 pings are done, I need it to return when the ping is successful. The program "say" is on OSX it makes the computer speak.

#!/bin/bash
echo begin ping
if ping -c 100000 8.8.8.8 | grep timeout;
then echo `say timeout`;
else echo `say the internet is back up`;
fi

OK I don't have rights to answer my own question so here's my answer for it after playing around:

Thanks, yeah I didn't know about $? until now. Anyway now I've gone and made this. I like that yours doesn't go forever but in my situation I didn't need it to stop until it's finished.

#!/bin/bash
intertube=0
echo "begin ping"
while [ $intertube -ne 1 ]; do
        ping -c 3 google.com
        if [ $? -eq  0 ]; then
                echo "ping success";
                say success
                intertube=1;
        else
                echo "fail ping"
        fi
done
echo "fin script"

Answer 1

I liked paxdiablo's script, but wanted a version that ran indefinitely. This version runs ping until a connection is established and then prints a message saying so.

echo "Testing..."

PING_CMD="ping -t 3 -c 1 google.com > /dev/null 2>&1"

eval $PING_CMD

if [[ $? -eq 0 ]]; then
    echo "Already connected."
else
    echo -n "Waiting for connection..."

    while true; do
        eval $PING_CMD

        if [[ $? -eq 0 ]]; then
            echo
            echo Connected.
            break
        else
            sleep 0.5
            echo -n .
        fi
    done
fi

I also have a Gist of this script which I'll update with fixes and improvements as needed.

Answer 2

You don't need to use echo or grep. You could do this:

ping -oc 100000 8.8.8.8 > /dev/null && say "up" || say "down"

Answer 3

If you use the -o option, Mac OS X’s ping will exit after receiving one reply packet.

Further reading: http://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man8/ping.8.html

EDIT: paxdiablo makes a very good point about using ping’s exit status to your advantage. I would do something like:

#!/usr/bin/env bash
echo 'Begin ping'
if ping -oc 100000 8.8.8.8 > /dev/null; then
    echo $(say 'timeout')
else
    echo $(say 'the Internet is back up')
fi

ping will send up to 100,000 packets and then exit with a failure status—unless it receives one reply packet, in which case it exits with a success status. The if will then execute the appropriate statement.

Answer 4

Here's my one-liner solution:

screen -S internet-check -d -m -- bash -c 'while ! ping -c 1 google.com; do echo -; done; echo Google responding to ping | mail -s internet-back [e-mail]'

This runs an infinite ping in a new screen session until there is a response, at which point it sends an e-mail to [e-mail]. Useful in the age of e-mail sent to phones.

(You might want to check that mail is configured correctly by just running echo test | mail -s test [e-mail] first. Of course you can do whatever you want from done; onwards, sound a bell, start a web browser, use your imagination.)

Answer 5

You probably shouldn't rely on textual output of a command to decide this, especially when the ping command gives you a perfectly good return value:

The ping utility returns an exit status of zero if at least one response was heard from the specified host; a status of two if the transmission was successful but no responses were received; or another value from <sysexits.h> if an error occurred.

In other words, use something like:

((count = 100))                            # Maximum number to try.
while [[ $count -ne 0 ]] ; do
    ping -c 1 8.8.8.8                      # Try once.
    rc=$?
    if [[ $rc -eq 0 ]] ; then
        ((count = 1))                      # If okay, flag to exit loop.
    fi
    ((count = count - 1))                  # So we don't go forever.
done

if [[ $rc -eq 0 ]] ; then                  # Make final determination.
    echo `say The internet is back up.`
else
    echo `say Timeout.`
fi

Answer 6

I use this Bash script to test the internet status every minute on OSX

#address=192.168.1.99  # forced bad address for testing/debugging
address=23.208.224.170 # www.cisco.com
internet=1             # default to internet is up

while true;
do
    # %a  Day of Week, textual
    # %b  Month, textual, abbreviated
    # %d  Day, numeric
    # %r  Timestamp AM/PM
    echo -n $(date +"%a, %b %d, %r") "-- " 
    ping -c 1 ${address} > /tmp/ping.$
    if [[ $? -ne 0 ]]; then
        if [[ ${internet} -eq 1 ]]; then   # edge trigger -- was up now down
            echo -n $(say "Internet down") # OSX Text-to-Speech
            echo -n "Internet DOWN"
        else
            echo -n "... still down"
        fi
        internet=0
    else
        if [[ ${internet} -eq 0 ]]; then     # edge trigger -- was down now up
            echo -n $(say "Internet back up") # OSX Text-To-Speech
        fi
        internet=1
    fi   
    cat /tmp/ping.$ | head -2 | tail -1
    sleep 60 ; # sleep 60 seconds =1 min
done