LinuxQuestions.org - How to get bash to wait for something to happen?

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How to get bash to wait for something to happen?

I have dial-up Internet access. I want to have a script do the following:

>Dialout to get ppp0 up
>Once ppp0 is up, run another script

This is what I've done: it works, but I don't like much:

Code:

#!/bin/bash

# User initiation of ppp0 Internet connection and setup of iptables

# Clear variable PTP

PTP=



while [ "$PTP" != "255.255.255.255" ]

do

  PTP=$( /sbin/ifconfig ppp0 | grep 'inet addr:' | gawk -F: '{ print $4 }' )

done



# Get present IP address:

THISIP=$( /sbin/ifconfig ppp0 | grep 'inet addr:' | gawk -F: '{ print $2 }' | gawk '{ print $1 }' )



# Setup iptables with new IP address

iptables -t mangle -F

iptables -t nat -F

iptables -t filter -F



/sbin/route del default

/sbin/route add default gw $THISIP



#*mangle

/sbin/iptables -t mangle -P PREROUTING ACCEPT

/sbin/iptables -t mangle -P INPUT ACCEPT

/sbin/iptables -t mangle -P FORWARD ACCEPT

...followed by all the other rules, some of which need the $THISIP variable...

This works, but the while command gets exectued as fast as it can until ppp0 comes up, maybe 100 times! I'd rather have it execute every 3 seconds or so and then I could do even better by exiting if I don't get ppp0 with 10 tries. I looked at 'watch' but I don't know how I could use that: maybe redirect the output to an if loop? But how is that done?

Thanks-

Have a look at /etc/ppp/ip-up, pppd launches this script when ppp0 is active

Otherwise as a general question how to make bash wait for an event, I don't know. I use the same solution for different events but you should add sleep 1 in the while loop.

Put sleep inside your loop. Man sleep.

Great work, guys! Sleep is what I asked for, but thanks, nx5000, I think /etc/ppp/ip-up.d is what I should look at. Another brick in the wall.

Cheers~

Quote:

and then I could do even better by exiting if I don't get ppp0 with 10 tries.

For this you need a counter inside the loop, one way to do it is with expr:

Code:

COUNTER=`expr COUNTER + 1`

if [ $COUNTER -gt 10 ]; then

  echo "No connection."

  exit 1

fi

Man expr gives you a detailed explanation on how expr works.