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Variables scope.

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# 1  
Old 05-22-2008
Variables scope.
Hi ,
I'm trying to change the variable value in a while loop , however its not working it seems that the problem with subshells while reading the file.

#!/bin/sh
FLAG=0;
cat filename | while read data
do
FLAG=1;
done

echo $FLAG

Should display 1 instead displays 0
# 2  
Old 05-22-2008
Quote:
Originally Posted by dinjo_jo
Hi ,
I'm trying to change the variable value in a while loop , however its not working it seems that the problem with subshells while reading the file.

#!/bin/sh
FLAG=0;
cat filename | while read data
do
FLAG=1;
done

echo $FLAG

Should display 1 instead displays 0
It will only display the value of FLAG as 1 when the condition is satisfied,that means there is some file you are trying to cat and reading lines. So check for the file first.

Thanks..
# 3  
Old 05-22-2008
The file exists , but since there is a while loop each reads a file , it creates a subshell , so the value is lost as soon as while loop ends.
# 4  
Old 05-22-2008
#!/bin/sh
FLAG=0;
while read data
do
FLAG=1;
done < filenname

echo $FLAG

try this u will get flag value 1
# 5  
Old 05-23-2008
Unfortunately that only works in bash shell.
# 6  
Old 05-23-2008
Bug checking for file existence first
Hi,

First yo chech for the file existence and then

FLAG=0;
while read file
do
FLAG =1;
done < input_file
echo "$FLAG"

I think this should work...
# 7  
Old 05-23-2008
There no single explanation and the main problem is not whether the file exists. It is what shell is being used. Consider this:

Code:
$ cat fcheck
#!/bin/sh

FLAG=0;
cat filename | while read data
do
echo "data=$data"
FLAG=1;
done

echo $FLAG

Bash
Code:
$ bash fcheck
data=line1
data=line2
0

Bourne:
Code:
$ sh fcheck
data=line1
data=line2
0

Korn:
Code:
$ ksh fcheck
data=line1
data=line2
1

So for sh, the behavior is as expected.
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