how to get the variable in while loop outside of it?

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how to get the variable in while loop outside of it?

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11-07-2011

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how to get the variable in while loop outside of it?

bash-3.00$ cat compare.sh
#NOTE : 1.Filename must not have space for the script to work.
# 2.Script wont work if symlinks are there instead of proper filenames.

Code:

#!/bin/bash
#set -x

#############################VERIFYING THE EXISTENCE OF DUPLICATE FILENAMES IN THE SUPPLIED FILENAMES ###############

if [[ $# -lt 1 ]];then
echo "Usage : `basename $0` filename" 1>&2
exit 2
fi
awk '{f=$9;
        for(i=10;i<=NF;i++)
           f=f" "$i;
           d[f]++;
     }
END{
        for(f in d)
                if(d[f] > 1)
                 printf("file %s occurs %d times\n",f,d[f]);
                                                    }' `basename $1`
echo -e  "Please remove the dupliacte entries,\
\nkeep the file with the latest timestamp and check again"

################################CHECKING SIZE,DATE,TIME,FILENAME WITH THE EXISTING FILES############################

status=0
cat $1 | awk '{print $(NF-4),"\t",$(NF-3),"\t",$(NF-2),"\t",$(NF-1),"\t",$(NF)}' | \
while read size mon day time filename; do
    if [[ ! -f "$filename" ]]; then
        echo "ERROR: no such file: $filename" >&2
        status=1
    else
        filesize=$(ls -lrt "$filename" | awk '{print $5}')
        if [[ "$size" != "$filesize" ]]; then
            echo "ERROR: size mismatch: $filename" >&2
            status=1
        else
           # filetime=$(ls -lrt "$filename" | awk '{print $6," ",$7," ",$8}')
                actual_mon=$(ls -lrt "$filename" | awk '{print $6}')
                actual_day=$(ls -lrt "$filename" | awk '{print $7}')
                actual_time=$(ls -lrt "$filename" | awk '{print $8}')
            if [[ "$mon $day $time" != "$actual_mon $actual_day $actual_time" ]]; then
                echo "ERROR: date mismatch: $filename" >&2
                status=1
            fi
        fi
    fi
done
echo $status
if [[ "$status" -eq 0 ]];then
echo -e "\t\n\nSuccess! All the files are found and their size and timestamp is also matching with the existing files."
else
echo -e "\t\n\nFailure! Non-matching files are found or file doesn't exist."
fi

The value of status always remains 0.
How do i get the changed value from inside the while loop

On the other hand :

Code:

bash-3.00$ cat scope.sh
#!/bin/bash
x=0
while [[ "$x" -lt 10 ]];do
x=$(($x+1))
done
echo $x

here, the value of x changes to 10

why is this deviation.

Please help me i need to access the changed value in the first script but i am unable to do it.

Last edited by Franklin52; 11-07-2011 at 06:03 AM.. Reason: Please use code tags for data and code samples, thank you

munish259272

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11-07-2011

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Code:

bash-3.00$ cat compare.sh
#NOTE : 1.Filename must not have space for the script to work.
#       2.Script wont work if symlinks are there instead of proper filenames.

#!/bin/bash
#set -x

#############################VERIFYING THE EXISTENCE OF DUPLICATE FILENAMES IN THE SUPPLIED FILENAMES ###############

if [[ $# -lt 1 ]];then
echo &quot;Usage : `basename $0` filename&quot; 1>&2
exit 2
fi
awk '{f=$9;
        for(i=10;i<=NF;i++)
           f=f&quot; &quot;$i;
           d[f]++;
     }
END{
        for(f in d)
                if(d[f] > 1)
                 printf(&quot;file %s occurs %d times\n&quot;,f,d[f]);
                                                    }' `basename $1`
echo -e  &quot;Please remove the dupliacte entries,\
\nkeep the file with the latest timestamp and check again&quot;

################################CHECKING SIZE,DATE,TIME,FILENAME WITH THE EXISTING FILES############################

status=0
cat $1 | awk '{print  $(NF-4),&quot;\t&quot;,$(NF-3),&quot;\t&quot;,$(NF-2),&quot;\t&quot;,$(NF-1),&quot;\t&quot;,$(NF)}'  | \
while read size mon day time filename; do
    if [[ ! -f &quot;$filename&quot; ]]; then
        echo &quot;ERROR: no such file: $filename&quot; >&2
        status=1
    else
        filesize=$(ls -lrt &quot;$filename&quot; | awk '{print $5}')
        if [[ &quot;$size&quot; != &quot;$filesize&quot; ]]; then
            echo &quot;ERROR: size mismatch: $filename&quot; >&2
            status=1
        else
           # filetime=$(ls -lrt &quot;$filename&quot; | awk  '{print $6,&quot; &quot;,$7,&quot; &quot;,$8}')
                actual_mon=$(ls -lrt &quot;$filename&quot; | awk '{print $6}')
                actual_day=$(ls -lrt &quot;$filename&quot; | awk '{print $7}')
                actual_time=$(ls -lrt &quot;$filename&quot; | awk '{print $8}')
            if [[ &quot;$mon $day $time&quot; != &quot;$actual_mon $actual_day $actual_time&quot; ]]; then
                echo &quot;ERROR: date mismatch: $filename&quot; >&2
                status=1
            fi
        fi
    fi
done
echo $status
if [[ &quot;$status&quot; -eq 0 ]];then
echo -e &quot;\t\n\nSuccess! All the files are found and their size  and timestamp is also matching with the existing files.&quot;
else
echo -e &quot;\t\n\nFailure! Non-matching files are found or file doesn't exist.&quot;
fi

Check out Variable Scope in Bash (NuclearDonkey.net) for one of several possible solutions here. Essentially, the issue is that you're modifying variables in a sub-process. You'll either need some inter-process trickery, or you'll have to modify your code to eliminate the direct use of the pipeline.

Also, please use [code] tags, as they make things much, much easier to read.

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This is an issue caused with the way bash implements pipes. When piping input to a while, I believe that bash executed the while in a child processes which causes any changes to variables inside of the while to be lost.

This is one reason I prefer kshell over bash. If you have a modern kshell, I suggest you use it. If not then try writing your output to a temp file and reading it into the while.

Code:

x=0
ls | while read f
do
    x=$(( $x + 1 ))
    printf "in loop: $x\n"
done
printf "after loop: $x\n"

 ls >/tmp/ls
x=0

 while read f
do
    x=$(( $x + 1 ))
    printf "in loop: $x\n"
done </tmp/ls
printf "after second loop: $x\n"

Try this in both shells to see the difference. Ksh gets the answer right after the loop both times.

Last edited by agama; 11-07-2011 at 12:45 AM.. Reason: typo

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Here is a little BASH trick to avoid these problems...

Code:

#!/bin/bash

function myLoop()
{
  echo $1 |
  while read WORD
  do
    echo $WORD|egrep "[0-9]" 2>/dev/null 1>/dev/null
    RETVAL=$?

    echo "Something to the screen..." >&2
    echo $RETVAL
  done
}

echo RETVAL=$(myLoop $1)

The basic idea is to echo the value as a function output. This output can then be captured as whatever variable you want.

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