I loose the variable value when I exit the while loop

[potro]

Hi,

j=0
grep "^Listen" httpd.conf | awk '{print $2}'|
while read var
do
eval "LPORT"$j=$var
eval echo "\$LPORT$j"
j=$[j+1]
done
echo $LPORT1

The echo inside the while works and prints the variable but the last echo of $LPORT1 (which insile while had a valid value) is empty.

Thanks,
Bianca

[vsemaska]

That's because piping the output to a while loop causes a child process to be spawned. When the loop finishes the child process is deleted thus losing the value. The only solution I found is to redirect the output to a file and do this:

j=0
grep "^Listen" httpd.conf | awk '{print $2}' > tmp.tmp
while read var
do
eval "LPORT"$j=$var
eval echo "\$LPORT$j"
j=$[j+1]
done < tmp.tmp
echo $LPORT1

[scm]

The easiest way to fix the problem is to change your shebang line from /bin/bash to /bin/ksh - Korn does it "properly".

[potro]

That's because piping the output to a while loop causes a child process to be spawned. When the loop finishes the child process is deleted thus losing the value. The only solution I found is to redirect the output to a file and do this:

j=0
grep "^Listen" httpd.conf | awk '{print $2}' > tmp.tmp
while read var
do
eval "LPORT"$j=$var
eval echo "\$LPORT$j"
j=$[j+1]
done < tmp.tmp
echo $LPORT1

Is then another solution to the problem: I grep a file and put the values in variables:
E.g.:
[root@skynet]# grep "^Listen" httpd.conf | awk '{print $2}'
FrontEnd_1_IP:8081
FrontEnd_2_IP:8081
8081
8082
8083

I need to create variables:
$LPORT1 with value FrontEnd_1_IP:8081
$LPORT2 with value FrontEnd_1_IP:8081
etc.

and I need to use this variables inside my script in other functions etc.

Your solution works ... but if the I enter another while or another function inside my script and I want to use the variables they don't have a value

Thanks a lot,
Bianca

[vsemaska]

The way your loop is set up your variables will start with LPORT0 not LPORT1. You have to move your 'j=$[j+1]' line before the 1st eval line to start with LPORT1.

Can you give an example of a script where it's not working? I tried it and the values are there within another loop.

#!/bin/bash -vx

j=0
grep "^Listen" httpd.conf | awk '{print $2}' > tmp.tmp
while read var
do
j=$[j+1]
eval "LPORT"$j=$var
eval echo "\$LPORT$j"
done < tmp.tmp
echo $LPORT1

j=0
while read
   do
        j=$[j+1]
        eval echo "\$LPORT$j"
   done < tmp.tmp

[potro]

The way your loop is set up your variables will start with LPORT0 not LPORT1. You have to move your 'j=$[j+1]' line before the 1st eval line to start with LPORT1.

Can you give an example of a script where it's not working? I tried it and the values are there within another loop.

#!/bin/bash -vx

j=0
grep "^Listen" httpd.conf | awk '{print $2}' > tmp.tmp
while read var
do
j=$[j+1]
eval "LPORT"$j=$var
eval echo "\$LPORT$j"
done < tmp.tmp
echo $LPORT1

j=0
while read
   do
        j=$[j+1]
        eval echo "\$LPORT$j"
   done < tmp.tmp

Hi

Indeed it works. I can't understand what I tested.

The issue I still have is to give this values to another variable:
j=0
while read
do
j=$[j+1]
NEWPORT="\$LPORT$j"
echo $NEWPORT
# I do something with the variable
done

NEWPORT variable has the values: $LPORT1, $LPORT2 and not the value of the variables.

Thanks,
Bianca

[vsemaska]

You forgot the eval.

eval NEWPORT="\$LPORT$j"

[potro]

You forgot the eval.

eval NEWPORT="\$LPORT$j"

Indeed.


Thanks a lot,
Bianca

[vsemaska]

It's because you directed the shell to get standard input (channel 0) from tmp.tmp with the command:

done < tmp.tmp

If you want to prompt for input from standard input then you have to read from tmp.tmp on a different channel. In this example I'll use channel 3.

j=0
i=0
exec 3<tmp.tmp # Open tmp.tmp for reading on channel 3
while read -u3 # Read from channel 3
do
j=$[j+1]
eval NEWLPORT="\$LPORT$j"
echo $ANEWLPORT
echo "Please type the Listen Port and F when finish : (current value:$NEWLPORT )"
read -e NEWLPORT
if [ "$NEWLPORT" != "F" ]
then
i=$[i+1]
eval "LISTEN_PORT"$i=$NEWLPORT
fi
done
exec 3<&- # Close channel 3.

[potro]

Thanks for your time.
With your help I managed to solve my script issue.

Have a nice day,
Bianca