Bash shell scripting

mravljica · 04-21-2009, 12:45 PM

Hi!

I am new to bash programing but the learning is in progress.
I have made a script which at scheduled times update local files from remote servers. I have created a file which contains server names eg.:
server1
server2
server3
server4
...

How do I make my script to choose the first server and if the first one is unreachable to select the next one, etc. and when it comes to the server which is reachable then start making update and then exit.
I think I need to use some sort of loop (for, while)???

I have only the part that check for reachability of the server:
-----------
case `ping -qnc 1 $server 2>&1` in
*'100% packet loss'*)
echo "Server unreachable."
exit 1
*'0% packet loss'*)
echo "Server ready"
$update
;;
esac
-----------

Thank you for your help in advance!

Regards,
Sasa

H_TeXMeX_H · 04-21-2009, 02:21 PM

I usually just use the:

Code:

while read line
do

done < file

to read files line by line for processing, especially when the file is short. So you could put your code inside that loop. I'm not sure about using ping for this, I suppose you could, but what if the server doesn't accept pings ?

mravljica · 04-22-2009, 04:24 AM

Ping will be accepted. So if I understood wright the script should look like the following:

Code:

servers = servers.txt

read $servers

while read line
do
  case `ping -qnc 1 $line 2>&1` in
       *'100% packet loss'*)
         echo "Server unreachable."
         exit 1
       *'0% packet loss'*)
         echo "Server ready"
         $update
         exit 0
       ;;
  esac
done < $servers
exit 0

Is this OK?

Regards,
Sasa

H_TeXMeX_H · 04-22-2009, 05:16 AM

What is the point of 'read $servers' ?

The other line should be:

Code:

servers=servers.txt

Libu · 04-22-2009, 06:18 AM

Instead of

Quote:

case `ping -qnc 1 $line 2>&1` in
*'100% packet loss'*)
echo "Server unreachable."
exit 1
*'0% packet loss'*)
echo "Server ready"
$update
exit 0
;;
esac

I would suggest

Quote:

[[ `ping -qnc 1 $line 2>&1` ]] && ( echo "Server Ready";exit 0 ) || ( echo "Server Unreachable"; exit 1 )

Libu · 04-22-2009, 06:37 AM

Hmm...i guess you would not want to exit if the server is unreachable, rather just echo and at the end, instead of "exit 0" user "exit 1" as control would go to the end only if all servers are unreachable.

mravljica · 04-22-2009, 07:05 AM

Quote:

Originally Posted by Libu

Hmm...i guess you would not want to exit if the server is unreachable, rather just echo and at the end, instead of "exit 0" user "exit 1" as control would go to the end only if all servers are unreachable.

You are wright. If the server is unreachable then I want to check the next in the line till the one that is reachable.

mravljica · 04-22-2009, 08:17 AM

The script is partially working.

Code:

while read line
do
  case `ping -qnc 1 $line 2>&1` in
       *'100% packet loss'* )
         echo "Server unreachable"
       ;;
       *'0% packet loss'* )
         echo "Server ready"
         # run function update
         update
         exit 1
       ;;
  esac
done < $servers
exit 0

partially I mean because it just run the loop but no echo is displayed if server is ready or unreachable. I ahve ran bash -x and only the loop is working then exit 0.

What am I missing here?

Regards,
Sasa

H_TeXMeX_H · 04-22-2009, 09:14 AM

This is what I would do:

Code:

#!/bin/sh

servers=servers.txt

while read line
do
  if test $(ping -nc 1 $line | grep packet | awk '{ print $6 }') == '0%'
  then
    echo "Server ready"
    # run function update
    update
	 
    # success
    exit 0
  else
    echo "Server unreachable"
  fi
done < $servers

# fail
exit 1

Libu · 04-22-2009, 09:26 AM

Quote:

servers="servers.txt"

while read line
do
echo "For Server: $line "
[[ `ping -qnc 1 $line 2>/dev/null` ]] && ( echo "Server Ready";update;exit 0 ) || ( echo "Server Unreachable")

done < $servers

exit 1

I would still prefer the one line solution

. But you should use H_TeXMeX_H's way for it to be portable. My way would only work if you are using bash (or ksh ??).

ntubski · 04-22-2009, 10:21 AM

@Libu: You need to use "{" instead of "("

Code:

ping -qnc 1 $line >/dev/null 2>&1 && { echo "Server Ready";update;exit 0; } || { echo "Server Unreachable"; }

"(" will open a subshell so the exit will not end the top level script. And getting rid of the [[ makes it portable to most shells, I think.

mravljica · 04-22-2009, 12:45 PM

Got my script working.

Thank you all for the help.

Regards,
Sasa

Libu · 04-22-2009, 02:11 PM

ntubski:
you are right about it spawning a new shell. thanks for pointing it out.