Does a variable lose its value outside the loop in shell script?

Shell Programming and Scripting
1

hi,

when we assign a variable inside a for loop or while loop in a shell script, does it loses its value after comming out of the loop. i am facing this issue.

can anyone help me??

2

loops create subshells when you pipe the output to while or for loops so you will loose the values..
use process substitution..

3

Hello,

The variable should have the last value which was assigned to it in loop.
Here is an example for it.

 
$ cat loop_example.ksh
str='monday, tuesday, wednesday, thursday, friday, saturday, sunday'
str1=`echo $str | sed 's/\,//g'`
set -A array_str ${str}

for i in ${array_str[@]}
do
a=$i

done

echo $a
 
 

$ ksh loop_example.ksh
sunday
$

We have a script named loop_example.ksh in which variable a have many values but if you will print it's value outside from loop it will show the last one as Sunday in the above example.

Thanks,
R. Singh

4

ya obviously, it will have the latest value since u r overwriting the previous value of $a inside the for loop.

my question is

cat file_names
sample.txt

shell_script_B.sh

echo "In shell_script_B.sh"
FILENAME="original.txt"
echo "FILENAME = {$FILENAME}"
echo ""
echo "-------Inside the loop-------"
cat file_names | while read line
do
        FILENAME=$line       # reassigning the FILENAME
        echo "FILENAME = {$FILENAME}"
done
echo "-------End loop--------------"
echo ""
echo "FILENAME = {$FILENAME}"

Output

In shell_script_B.sh
FILENAME = {original.txt}

-------Inside the loop-------
FILENAME = {sample.txt}
-------End loop--------------

FILENAME = {original.txt}

check the output. Inside the Loop it prints the new value and outside the value it prints original file. what is the solution for this??

5

Pleas read my reply to your thread.. since you are piping the out put to while it will open a subshell and variable value would be lost once its back to main shell

use
while read line ; do
blah blah
blah
done < filename

1 Like
6

Hello,

Could you please the following if this helps.

 
 
$ cat script_user_error.ksh
echo "In shell_script_B.sh"
FILENAME="original.txt"
echo "FILENAME = {$FILENAME}"
echo ""
echo "-------Inside the loop-------"
while read line
do
        FILENAME=$line       # reassigning the FILENAME
        echo "FILENAME = {$FILENAME}"
done < "file_names"

echo "-------End loop--------------"
echo ""
echo "FILENAME = {$FILENAME}"
 
 

$ ksh script_user_error.ksh
In shell_script_B.sh
FILENAME = {original.txt}
-------Inside the loop-------
FILENAME = {sample.txt}
-------End loop--------------
FILENAME = {sample.txt}
$

I have just made the changes in color. Is it meets your requirement.
Kindly let me know if I can help on same.

Thanks,
R. Singh

1 Like
7

i read your thread before also and i got the problem what you said. i just wanted a solution for that. so this code will do the same task what i want. thanks.

8

Its the way shell behaves if you dont wanna change anything and still want it to work then sorry its not the way shell designed :slight_smile:

either change the way you are using while loop or make export $FILENAME

9

i have changed the way you told and its working fine..

1 Like