I loose the variable value when I exit the while loop

05-08-2008	#1 (permalink)
potro Just Joined! Join Date: Mar 2008 Posts: 30	I loose the variable value when I exit the while loop 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

05-08-2008	#2 (permalink)
vsemaska Linux User Join Date: Jun 2007 Posts: 318	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: Code: 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

05-08-2008	#3 (permalink)
scm Linux Engineer Join Date: Feb 2005 Posts: 1,004	The easiest way to fix the problem is to change your shebang line from /bin/bash to /bin/ksh - Korn does it "properly".

05-09-2008

#4 (permalink)

potro

Just Joined!

Join Date: Mar 2008

Posts: 30

Quote:

Originally Posted by 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:

Code:

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

05-10-2008	#5 (permalink)
vsemaska Linux User Join Date: Jun 2007 Posts: 318	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. Code: #!/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

05-12-2008

#6 (permalink)

potro

Just Joined!

Join Date: Mar 2008

Posts: 30

Quote:

Originally Posted by 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.

Code:

#!/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

05-12-2008	#7 (permalink)
vsemaska Linux User Join Date: Jun 2007 Posts: 318	You forgot the eval. eval NEWPORT="\$LPORT$j"

05-12-2008

#8 (permalink)

potro

Just Joined!

Join Date: Mar 2008

Posts: 30

Quote:

Originally Posted by vsemaska

You forgot the eval.

eval NEWPORT="\$LPORT$j"

Indeed.

Thanks a lot,
Bianca

05-12-2008

#9 (permalink)

vsemaska

Linux User

Join Date: Jun 2007

Posts: 318

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.

Code:

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.

05-14-2008	#10 (permalink)
potro Just Joined! Join Date: Mar 2008 Posts: 30	Thanks for your time. With your help I managed to solve my script issue. Have a nice day, Bianca