bash script for network restart

munkeh · 11-09-2003, 12:59 PM

I am only 3 days into learning bash scripts, so bear
with me. I have encountered a problem I cannot solve
by reading tutorials.

This script produces a syntax error in the case statement
inside the function named "direction"

Code:

./nrs: line 37: syntax error near unexpected token `;;'
./nrs: line 37: `;;'

nrs is the filename of the script.

Well, here it is. Very q&d

Code:

#!/bin/bash
#
# v1.0
# This script is designed as a temporary fix for
# the internet connection dropout problem.
#
# Unitil such time as the fault can be properly
# diagnosed, this will be the fix.
#
# The network and iptables firewall should be
# reset when the connection loss is detected by
# the ping_eval() function in the script.
#
# The final script will be executed by the
# system (as a service?)as it will reside in
# /etc/rc.d/init.d/
#


				## Functions ##
function ping_eval()
{
	until [ $? != "0" ] # till ping returns a fail value for its exit status
		do
		sleep 30
		ping -c 1 194.168.8.100 -w 3 # ping again
		done
}



function direction()
{
case "$?" in
"0")
		ping_eval()
;;

"1")
	/etc/rc.d/init.d/network restart 	#restarts the network
	/etc/rc.d/stronger_firewall-2.4 restart #restarts the firewall
;;

"2")
	## 	/home/ian/logs/nrs/fail < cat <<- _EOF_		# will eventually print
	##	echo "ping has generated an error at"  		# the time of the exit status 2
	##	date						# from ping when I figure out how.
	##	echo "the nrs has exited due to this error"
	##	_EOF_
	exit 1 #if the ping returns an unknown error
;;

esac
}



				## Commands ##

case "$1" in
start)
	ping -c 1 194.168.8.100 -w 3 # ping again


	until [ $? = "3" ]
		do
	                direction()
	        done

	exit 0
;;

*)
        echo "Usage: nrs {start}"
	exit 1
;;
esac
# end of script

I'm sure its something glaringly obvious but I've
gone over case statement syntax again and again,
and I just can't fathom it.

Any help would be greatly appreciated

/bin/bash · 11-09-2003, 05:47 PM

When you are calling the function remove the parenthesis, e.g.

ping_eval() change to ping_eval @ line 37
direction() change to direction @ line 68

munkeh · 11-10-2003, 09:51 AM

Thank you so much. I thought it would be something o so simple.
I do like forums such as these.

munkeh · 11-10-2003, 12:24 PM

Code:

ping -c 1 194.168.8.100 -w 3 # ping again
	echo "\"?\" is $?"

	until [ $? = "127" ]
	        do
	                echo "\"?\" is $?"
		sleep 5
		direction
	        done

now it changes the ? variable to 1 between

Code:

until

and

Code:

echo "\"?\" is $?"

I don't see how
Argh, coding scripts is harder than anticipated

jim mcnamara · 11-10-2003, 01:29 PM

I'm not sure what you're asking, so I'm guessing - and
changing your code which may not be the best, but it's how you'll learn.

Code:

#! /usr/bin/sh
        ping -c 1 194.168.8.100 -w 3 # ping again
        retval=$?
        echo " retval=$retval"

        while [ true ]   # change this to test retval instead, if needed
	        do
	           echo "retval =$retval"
	           if [ $retval -eq 127 ]; then 
	                break;
	           fi
	           sleep 5
	           direction
	           retval=$?
	        done

munkeh · 11-10-2003, 03:47 PM

Thank you.

I still don't understand what command returns an exit status of 1
whithin that small part of code.

I'll try the code you suggest.

Thanks again

munkeh

/bin/bash · 11-10-2003, 04:36 PM

You need to look at the flow of your original code. I thought it had problems but I only answered the original question and I left the debugging to you.

Your program starts here:
case "$1" in
start)
ping -c 1 194.168.8.100 -w 3 # ping again
until [ $? = "3" ]
do
direction
done
exit 0

That first ping does nothing. It returns a $? but that is never checked before you call direction(). So the until loop is only checking the return value of direction(). However; you do not have a return from direction() only an exit 1, so direction() will never return to the original until loop (an exit statement terminates the script even if it is within a function.)

You don't have proper flow. You need to write down on paper what you want to do and try to make the code flow a little better.

Here is a rough draft:

Check input to see if how program was called.
You could also put an option to stop the script since it needs to be put in an endless loop.

Start -> MainLoop
Stop -> killall -9 $0
Unknown -> Exit with message

MainLoop() {
Start a while or untill loop
do
ping router
ping OK do nothing
ping Not OK do something
ping Unknown exit with error
done
}

/bin/bash · 11-10-2003, 04:43 PM

Here's an example.

Code:

#!/bin/bash
#
# v1.0
# This script is designed as a temporary fix for
# the internet connection dropout problem.
#
# Unitil such time as the fault can be properly
# diagnosed, this will be the fix.
#
# The network and iptables firewall should be
# reset when the connection loss is detected by
# the ping_eval() function in the script.
#
# The final script will be executed by the
# system (as a service?)as it will reside in
# /etc/rc.d/init.d/
#

main_loop() { 
while true
do
sleep 30
ping -c 1 194.168.8.100 -w 3 # ping again
case "$?" in
	0)
	echo "Ping OK, do nothing..."
	;;

	1)
	echo "Error 1"
	echo "Ping Not OK..." 	#restarts the network
	;;

	2)
	echo "Error 2"
	echo "the nrs has exited due to error #2"
	##	_EOF_
	return 2 #if the ping returns an error2
	;;

	*)
	echo "Error $?"
	echo "Unknown error..."
	return "$?"
	;;
esac
done
}

				## Commands ##

case "$1" in
    start)
	main_loop
        exit "$?"
	;;
    stop)
	killall -9 $0
	;;
        *)
        echo "Usage: nrs {start || stop}"
	exit 1
	;;
esac
# end of script

jim mcnamara · 11-10-2003, 05:00 PM

By default or design -

when a unix command fails it returns non-zero, almost always one ( 1 ).
when a unix command succeeds it returns a zero.

For every command the shell processes, it sets the internal variable $? to a 1 or a zero. The only things that return errors other than one are usually specialty code, not the standard GNU stuff.

Since commands that fail may still produce some output, or do some parts of what they are supposed to do - eg., tset does this, but if and when it fails it bombs with a one.

So, the only way to be positive that your command did not bomb is to test the return value.

If you are having trouble determining where in the script the error occurs -
make your first line
set -x

Be sure to turn this off as it produces way too much clutter to be run in production.