I know computers don't misbehave.
But I'm puzzled by what's happening right know in a script :
I simplified the example to point out what seems weird to me.
Don't try to find any sense to this stupid script.
There are 10 rows in /tmp/tmp.txt
Code:
i=0
tmpfile=/tmp/tmp.txt
while read -r; do
echo "$REPLY" > /dev/null
sed "1,$((++i))d" $tmpfile | wc -l
done < $tmpfile
Code:
i=0
tmpfile=/tmp/tmp.txt
while read -r; do
echo "$REPLY" > /dev/null
sed "1,$((++i))d" $tmpfile > /tmp/output; wc -l /tmp/output
done < $tmpfile
In the first script, I count line from the output of sed. In the second one, I first output sed to a file and then count the lines of that file.
I see no reason why the output would be different... YET:
The first script is running sed in a subshell environment; the second is not. The subshell is a byproduct of the shell's pipeline implementation. The difference is that when $i is incremented in a subshell, the new value is not available in the parent shell.
One workaround would be to increment the variable prior to calling sed.
Regards,
Alister
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10-02-2012
