[SOLVED] A little bash problem

Ziddy · 06-15-2012, 09:34 PM

Hey, I need some help with bash. I'm sure I'm gonna explain this in the most confusing way possible, so hopefully someone understands. I have two variables. $NAMES and $HOSTS. I'm using a for-loop. Each loop, it goes to the next in the $NAMES list, but I also want it to do the same for $HOSTS, without executing the code in the loop twice, or jumping to the very end of the list of the 2nd variable. (Which is what happens when I use two for-loops). I've tried...
for myName in $NAMES && for myHost in $HOSTS do
and a bunch of other combinations.. Brackets, pipes, semi-colons...
I want $NAMES and $HOSTS to stay in the same position as each other.
If $NAMES is on the 2nd in the list, so should $HOSTS.

Thanks for reading, and I'm sorry if I've confused you!
It seems like it should be so simple, but it's causing me quite a bit of problems.

pixellany · 06-15-2012, 09:42 PM

You say you want to go to different items in these two variables----what separates the items?---eg commas, colons, line feeds...etc.

It seems to me that you might be better off with arrays rather than a bunch of fields in variable name. With arrays, you just run a counter in your main loop, then use $counter to index into the arrays.

Ziddy · 06-15-2012, 09:52 PM

Well the for-loop goes to the next one in the variable, correct? It works fine with just one, but with two it doesn't.
Hrm. Lemme show you an example.

$NAMES="hi blah blarg"
$HOSTS="ip1 ip2 ip3"

for myName in $NAMES
do
for myHost in $HOSTS
do
if [ ${count:-0} -eq 0 ] || [ -z "$count" ]; then
echo -e "Host "$myName" ($myHost) is\t \033[31mOFFLINE\033[0m $(date)"
else
echo -e "Host "$myName" ($myHost) is\t \033[32mONLINE!\033[0m $(date)"
fi
done
done

This works fine, except $myName skips to the very last one in the list, when I want it to stay with $myHost.

edit: I'm sure I'm over-thinking this :\

pixellany · 06-15-2012, 10:29 PM

Quote:

Well the for-loop goes to the next one in the variable, correct?

It does?---have your tried it?

Regardless, you have 2 nested loops---for each pass thru the outer loop, you'll go thru all the iterations of the inner loop. I don't think that's what you had in mind...

pixellany · 06-15-2012, 10:33 PM

You are right--I was not thinking
here's the test:

Code:

[mherring@herring-lap play]$ var="one two three four"
[mherring@herring-lap play]$ echo $var
one two three four
[mherring@herring-lap play]$ for item in $var; do echo $item; done
one
two
three
four

Ziddy · 06-15-2012, 10:54 PM

Let me provide two examples: One without the $NAMES, one with, including the code.

Without (Output, followed by code)

Host (121.121.121.121) is OFFLINE Fri Jun 15 23:44:10 EDT 2012
Host (222.222.222.222) is ONLINE! Fri Jun 15 23:44:10 EDT 2012
Host (111.111.111.111) is OFFLINE Fri Jun 15 23:44:20 EDT 2012

#HOSTS="121.121.121.121 222.222.222.222 111.111.111.111"

for myHost in $HOSTS
do
count=$(ping -c $COUNT $myHost | grep 'received' | awk -F',' '{ print $2 }' | awk '{ print $1 }')
if [ ${count:-0} -eq 0 ] || [ -z "$count" ]; then
echo -e "Host ($myHost) is\t \033[31mOFFLINE\033[0m $(date)"
else
echo -e "Host ($myHost) is\t \033[32mONLINE!\033[0m $(date)"
fi
done

-----------------------------
With (followed by code)

$HOSTS="121.121.121.121 222.222.222.222 111.111.111.111"
$NAMES="AKILL RANDOM FILLER BUTTSECKS"

count=$(ping -c $COUNT $myHost | grep 'received' | awk -F',' '{ print $2 }' | awk '{ print $1 }')

#Check to see if ping was successful and display. With CoLoRzZz!

if [ ${count:-0} -eq 0 ] || [ -z "$count" ]; then
echo -e "Host $myName ($myHost) is\t \033[31mOFFLINE\033[0m $(date)"
else
echo -e "Host $myName ($myHost) is\t \033[32mONLINE!\033[0m $(date)"
fi
done
done

Host AKILL (121.121.121.121) is OFFLINE Fri Jun 15 23:51:39 EDT 2012
Host RANDOM (121.121.121.121) is OFFLINE Fri Jun 15 23:51:49 EDT 2012
Host FILLER (121.121.121.121) is OFFLINE Fri Jun 15 23:51:59 EDT 2012
Host BUTTSECKS (121.121.121.121) is OFFLINE Fri Jun 15 23:52:09 EDT 2012
Host AKILL (222.222.222.222) is ONLINE! Fri Jun 15 23:52:09 EDT 2012
Host RANDOM (222.222.222.222) is ONLINE! Fri Jun 15 23:52:09 EDT 2012
Host FILLER (222.222.222.222) is ONLINE! Fri Jun 15 23:52:10 EDT 2012
Host BUTTSECKS (222.222.222.222) is ONLINE! Fri Jun 15 23:52:10 EDT 2012
Host AKILL (111.111.111.111) is OFFLINE Fri Jun 15 23:52:20 EDT 2012
Host RANDOM (111.111.111.111) is OFFLINE Fri Jun 15 23:52:30 EDT 2012

As you can see, the names dont stay in sync with the hosts as they should.
I think you're correct about using arrays.
Hrm..

Ziddy · 06-16-2012, 12:23 AM

Alright, I figured it out. *flicks sweat*
Sorta glad I didn't get a direct answer, was able to figure it out by trail and error.
I'm sure it isn't the best way, but it works.

ii=0
for i in "${HOSTS[@]}"
do
count=$(ping -c $COUNT $i | grep 'received' | awk -F',' '{ print $2 }' | awk '{ print $1 }')

if [ ${count:-0} -eq 0 ] || [ -z "$count" ]; then
echo -e "Host ${NAMES[$ii]} ($i) is\t \033[31mOFFLINE\033[0m $(date)"
else
echo -e "Host ${NAMES[$ii]} ($i) is\t \033[32mONLINE!\033[0m $(date)"
fi

if [ "$ii" -eq ${#HOSTS[*]} ]; then
$ii=0
else
let "++ii"
fi

ntubski · 06-16-2012, 09:22 AM

The best way to check if systems are online is using nmap:

Code:

~$ HOSTS=(192.168.2.1 192.168.2.2)
~$ nmap -v -sn -oG - "${HOSTS[@]}" | grep -v '^#'
Host: 192.168.2.1 (mymodem)	Status: Up
Host: 192.168.2.2 ()	Status: Down

The -sn option says to only do a ping scan, but nmap has a lot more ways to check a host. Note that a system can be online but ignore pings, so a test with ping will think it is offline.

Adding names and formatting:

Code:

#!/bin/bash

NORMAL=$(tput setaf 0)
RED=$(tput setaf 1)
GREEN=$(tput setaf 2)

HOSTS=(192.168.2.1 192.168.2.2)
declare -A NAMES
NAMES[192.168.2.1]=router
NAMES[192.168.2.2]=non-existent-host

while read _ ip _ _ status ; do
    echo -en "Host ${NAMES[$ip]} ($ip) is\t "
    if [ "$status" = Down ] ; then
        echo -n "${RED}OFFLINE"
    else
        echo -n "${GREEN}ONLINE!"
    fi
    echo "${NORMAL} $(date)"
done < <(nmap -v -sn -oG - "${HOSTS[@]}" | grep -v '^#')

Code:

~/tmp$ ./scan.bash
Host router (192.168.2.1) is	 ONLINE! Sat Jun 16 10:05:05 EDT 2012
Host non-existent-host (192.168.2.2) is	 OFFLINE Sat Jun 16 10:05:05 EDT 2012

PS please use [code][/code] tags when posting code.

schneidz · 06-16-2012, 09:34 AM

Quote:

Originally Posted by Ziddy

Hey, I need some help with bash. I'm sure I'm gonna explain this in the most confusing way possible, so hopefully someone understands. I have two variables. $NAMES and $HOSTS. I'm using a for-loop. Each loop, it goes to the next in the $NAMES list, but I also want it to do the same for $HOSTS, without executing the code in the loop twice, or jumping to the very end of the list of the 2nd variable. (Which is what happens when I use two for-loops). I've tried...
for myName in $NAMES && for myHost in $HOSTS do
and a bunch of other combinations.. Brackets, pipes, semi-colons...
I want $NAMES and $HOSTS to stay in the same position as each other.
If $NAMES is on the 2nd in the list, so should $HOSTS.

Thanks for reading, and I'm sorry if I've confused you!
It seems like it should be so simple, but it's causing me quite a bit of problems.

Code:

echo $HOSTS | awk '{print $i}'