Variables scope.

dinjo_jo · #1 (**permalink**) 05-22-2008

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

namishtiwari · #2 (**permalink**) 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..

dinjo_jo · #3 (**permalink**) 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.

subin_bala · #4 (**permalink**) 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

dinjo_jo · #5 (**permalink**) 05-22-2008

Unfortunately that only works in bash shell.

abhisek.says · #6 (**permalink**) 05-23-2008

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...

rikxik · #7 (**permalink**) 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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