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Unix shell: workaround for loop problem

It’s not possible to get the value of the loop variables in some versions of ksh.

Example:

#!/bin/ksh

num=0
cat $0 | while read line ; do
 let num=num+1
done

echo "Number=$num"

This script will return “Number=0” as the result on some Linux machines.

Here is the workaround for the problem: You should change the redirection method for the input file.

#!/bin/ksh

l=0
while read line ; do
 let l=l+1
done < $0

echo "Number=$l"

The last script will return the correct result: “Number=9”

Another possibility is to use the named pipe:

#!/bin/ksh

TMPPIPE=/tmp/thepipe.$$
mkfifo $TMPPIPE
cat $0 > $TMPPIPE &
num=0
while read line ; do
 let num=num+1
done < $TMPPIPE

echo "Number=$num"

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