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

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 = 60))                           # 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 loop exit.
    else
        sleep 1                          # Minimise network storm.
    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 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

This can also be done with a timeout:

# Ping until timeout or 1 successful packet
ping -w (timeout) -c 1

Answer 4

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

Answer 5

If you use the -o option, BSD ping (which is also on macOS) will exit after receiving one reply packet.

Further reading: https://www.freebsd.org/cgi/man.cgi?query=ping

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.

EDIT 2: Chris points out that my logic is reversed, which is just embarrassing. Additionally, the echo commands (inherited from the question) serve no purpose, and there's no need to require bash specifically. I'm disappointed in 12-years-ago me. Today I would write:

#!/bin/sh
if ping -oc 100000 8.8.8.8 >/dev/null; then
    say 'the Internet is back up'
else
    say timeout
fi

Answer 6

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 my-email@example.com'

This runs an infinite ping in a new screen session until there is a response, at which point it sends an e-mail to my-email@example.com. 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 my-email@example.com first. Of course you can do whatever you want from done; onwards, sound a bell, start a web browser, use your imagination.)

Answer 7

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.