[SOLVED] Continuously append to same variable in for loop

keif · 08-29-2014, 10:31 AM

Hello, I am trying to retrieve a list of ssg hosts on my network via ping. I want to put the list into a single variable if possible, but I can't seem to figure out how to do this.

What I used to do is put them into a file, but I wanted to see if there was a way to put them all into the same variable instead.

Here is the format that I am using to do this, which is incorrect, as each time the variable is going to become whatever host was last $i

Code:

[techs@ts-01 ~]$ for i in `cat /etc/storelist | awk '{print $1}'`
> do
> ping -c 1 $i-ssg > /dev/null 2>/dev/null
> pingRet=$?
> if [ $pingRet -eq 0 ]; then
> ssgHost=`echo $i`
> fi
> done

I'm hoping there is a command available that handles this sort of thing. I am killing my brain trying to figure out how to make it work by tossing variables around:

i.e.

Code:

oldVar=`echo $newVar`
newVar=`echo $i`
bothVar=`echo $oldVar && echo $newVar`
allVar=`echo $bothVar &&  # here I'm stuck in logic, intellect and patience

If this variable tossing can work, I cannot seem to see the solution. I was hoping to get some input on this.

Thanks in advance.

westy500 · 08-29-2014, 10:48 AM

Variable arrays may help.

e.g.

Code:

a=0
for i in `cat /etc/storelist | awk '{print $1}'`
do
    ping -c 1 $i-ssg > /dev/null 2>/dev/null
    if [[ $? -eq 0 ]]
    then
        ssgHosts[$a]=$i
        let a=$a+1
    fi
done

echo ${ssgHosts[*]}

You can then use the array as you please...

Code:

for x in ${ssgHosts[*]}
do
    echo $x
done

Hope this helps.

Or, if you must use a single variable and not an array:

Code:

for i in `cat /etc/storelist | awk '{print $1}'`
do
    ping -c 1 $i-ssg > /dev/null 2>/dev/null
    if [[ $? -eq 0 ]]
    then
        ssgHosts="${ssgHosts} ${i}"
    fi
done

keif · 08-29-2014, 11:41 AM

Quote:

Originally Posted by westy500

Variable arrays may help.

e.g.

Code:

a=0
for i in `cat /etc/storelist | awk '{print $1}'`
do
    ping -c 1 $i-ssg > /dev/null 2>/dev/null
    if [[ $? -eq 0 ]]
    then
        ssgHosts[$a]=$i
        let a=$a+1
    fi
done

echo ${ssgHosts[*]}

You can then use the array as you please...

Code:

for x in ${ssgHosts[*]}
do
    echo $x
done

Hope this helps.

Or, if you must use a single variable and not an array:

Code:

for i in `cat /etc/storelist | awk '{print $1}'`
do
    ping -c 1 $i-ssg > /dev/null 2>/dev/null
    if [[ $? -eq 0 ]]
    then
        ssgHosts="${ssgHosts} ${i}"
    fi
done

westy, thanks so much!

Not only does this solve several issues, current and future, but it heads me down a path for greater learning.

Have a great weekend.

grail · 08-29-2014, 12:04 PM

Do not read data using a for loop, especially as it already has white space in it seeing you are then using awk to retrieve data.

Second, awk is quite capable of reading from a file so cat is of zero help.

Lastly, if you simply wish to append new items to an array, increasing an index is not required unless it is not to be a uniform array.

So with that all said:

Code:

while read -r ip _
do
  if ping -c 1 "$i-ssg" &>/dev/null
  then
    ssgHosts+=( "$ip" )
  fi
done</etc/storelist