Break command

venkidhadha · #1 (**permalink**) 01-23-2009

have a query on this break. I am using a program where I am using a while loop to execute it. It will get into a file take the first file and then ping it and if the ip is reachable then it will mail. Now what happens is that when i ping the ip it does nopt come out of the loop and it says "reply from reply from" . I need to usse a break statemetn to come out of this. Can you assist me in this.

Let me know if i need to explain more.

bakunin · #2 (**permalink**) 01-23-2009

To really help you with your problem it would be best to post your code - otherwise we are just left to guessing what the error might be.

Generally speaking it is better to not use "break" at all: it is basically a "GOTO" (in fact it is a "GOTO END OF LOOP", which is a hallmark of unstructured programming. You might want to read the famous article A Case against the GO TO statement by Edsger W. Dijkstra to better understand why this is bad practice.

The same is true, btw., for the "continue" statement.

I hope this helps.

bakunin

cfajohnson · #3 (**permalink**) 01-24-2009

Quote:

Originally Posted by bakunin

To really help you with your problem it would be best to post your code - otherwise we are just left to guessing what the error might be.

Absolutely!

Quote:

Generally speaking it is better to not use "break" at all: it is basically a "GOTO" (in fact it is a "GOTO END OF LOOP", which is a hallmark of unstructured programming. You might want to read the famous article A Case against the GO TO statement by Edsger W. Dijkstra to better understand why this is bad practice.

The same is true, btw., for the "continue" statement.

Nonsense!

Lakris · #4 (**permalink**) 01-24-2009

And by the way,
why the hangup about GOTO?
It is of course up to the programmer to construct legible and functional code, and for a small program or asm it is very useful. AND can be very readable too. Of course it is silly to use GOTO in a large program where it's hard to keep track of the state of things. But everything's not black and white.

/Lakris

venkidhadha · #5 (**permalink**) 02-10-2009

Here is the code snippet which i am using . actually wheen it tries to ping a node it pings it and then ig et a message sayng " Time exceeded" then it doesent come outside of the loop, which triggers more than 50 mails in 5 secs. Please advice

Code:

i=1
while [ $i -le 7 ]
do
     k=`cat iplist |head -$i|tail -1`
     ping $k
     if [$? -eq 0]
          then echo " The node $k is alive " |  mailx -s " Network connectivity " venki_dadad @in.com
          else echo " The node $k is down  " | mailx -s " Network connectivity " venki_dadad @in.com
          i=`expr $i + 1`
          echo $i
     fi
done

Lakris · #6 (**permalink**) 02-10-2009

Quote:

Originally Posted by venkidhadha

i=1
while [ $i -le 7 ]
do
k=`cat iplist |head -$i|tail -1`
ping $k
if [$? -eq 0]
then echo " The node $k is alive " | mailx -s " Network connectivity " venki_dadad @in.com
else echo " The node $k is down " | mailx -s " Network connectivity " venki_dadad @in.com
i=`expr $i + 1`
echo $i
fi
done

Hi, did You read my previous post about ping?
I can think of a few problems with Your code, but let's be systematic

1) If You have a list of hosts in a file, if iplist is a list of k's, then use that as a basis for Your loop and don't construct some strange mechanism that force You to change Your code just because the list changes.

Example:

Code:

while read k ; do
... some action here based on value of k ...
done < iplist

2) If You are on a *nix system, ping by default will continue to ping until You tell it to stop, so You must give it a condition so it's behaviour is predictable. As I said before. That IS Your break.

Example:

Code:

ping -c 1 $k

3) You can't have a space in the e-mail address, is it a typo? Make a habit of copy/paste when You submit code examples, otherwise it's very easy to make spleling mistakes.

And if You really want to know the status of the nodes, what is most important about it? To know if it's down? Maybe it's not very interesting to know that things are working as they should? Because, well, they should. Then just send a mail when a node is unreachable.

And if it's really important, why not put that information in the header, so it stands out?

Example:

Code:

while read k ; do
ping -c 1 $k &> /dev/null || echo "$k is DOWN, I repeat, $k is DOWN" |mailx -s "$k is DOWN" me@host 
done < iplist

which means, "if the ping command isn't successful ( || is an "else" ), then send me a mail about it". Try && for a different outcome...

Best regards,
Lakris

ddreggors · #7 (**permalink**) 02-10-2009

Quote:

Originally Posted by venkidhadha

i=1
while [ $i -le 7 ]
do
k=`cat iplist |head -$i|tail -1`
ping $k
if [$? -eq 0]
then echo " The node $k is alive " | mailx -s " Network connectivity " venki_dadad @in.com
else echo " The node $k is down " | mailx -s " Network connectivity " venki_dadad @in.com
i=`expr $i + 1`
echo $i
fi
done

Assuming you only want the first 7 IP's from this file, try this also:

Code:

ips=`head -n 7 iplist`
for myip in $ips
do
     ping -c 1 $myip
     if [$? -eq 0]
     then 
         echo " The node $myip is alive " |  mailx -s " Network connectivity " venki_dadad @in.com 
     else 
         echo " The node $myip is down  " | mailx -s " Network connectivity " venki_dadad @in.com 
      fi
done

Or you could batch this in one shot like this:

Code:

ips=`head -n 7 iplist`
RESULT=""
for myip in $ips
do
     # Make this post to the console (remove the '2>&1 >> /dev/null' at the end)  or leave it so that it is quiet
     ping -c 1 $myip 2>&1 >> /dev/null
     if [$? -eq 0]
     then 
         RESULT="${RESULT} \nThe node $myip is alive "  
     else 
         RESULT="${RESULT} \nThe node $myip is down  " 
      fi
done
echo -e "${RESULT}" |  mailx -s " Network connectivity " venki_dadad @in.com

One email sent with all test results.

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