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For loop not bringing variable back properly

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Join Date: Sep 2008

Posts: 2

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gornhorse

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Newbie Poster

For loop not bringing variable back properly

Feb 9th, 2009

Hi, I have two shell scripts that do the same thing, but are written differently. The first one works:

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size=0
pattern=foo
 
for file in *
do
	[ ! -f $file ] && continue
 
	if grep $pattern $file > /dev/null
	then
		tsize=`cat $file |wc -c`
		size=`expr $size + $tsize`
		echo "size is: $size"
	fi
done
echo "Total size of files containing $pattern is: $size"
size=0
pattern=foo

for file in *
do
	[ ! -f $file ] && continue
	
	if grep $pattern $file > /dev/null
	then
		tsize=`cat $file |wc -c`
		size=`expr $size + $tsize`
		echo "size is: $size"
	fi
done
echo "Total size of files containing $pattern is: $size"

With the output of

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 Shell Scripting Syntax (Toggle Plain Text) 
$ ./foofinder
size is: 34
size is: 77
size is: 223
size is: 478
size is: 758
size is: 855
Total size of files containing foo is: 855
$ ./foofinder
size is: 34
size is: 77
size is: 223
size is: 478
size is: 758
size is: 855
Total size of files containing foo is: 855

But, I then have this script:

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pattern=foo
total=0
 
ls -l | while read j1 j2 j3 j4 fsize j5 j6 j7 fname 
do
	[ ! -f $fname ] && continue
 
	if grep $pattern "$fname" > /dev/null 2>%1
	then
		total=`expr $total + $fsize`
		echo "size is: $total"
	fi
done
echo "Total size of files containing $pattern is: $total"
pattern=foo
total=0

ls -l | while read j1 j2 j3 j4 fsize j5 j6 j7 fname 
do
	[ ! -f $fname ] && continue

	if grep $pattern "$fname" > /dev/null 2>%1
	then
		total=`expr $total + $fsize`
		echo "size is: $total"
	fi
done
echo "Total size of files containing $pattern is: $total"

With the output of

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 Shell Scripting Syntax (Toggle Plain Text) 
$ ./foofinder2
size is: 34
size is: 77
size is: 223
size is: 478
size is: 758
size is: 855
Total size of files containing foo is: 0
$ ./foofinder2
size is: 34
size is: 77
size is: 223
size is: 478
size is: 758
size is: 855
Total size of files containing foo is: 0

Basically, I want to know why the second script returns the line:

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Total size of files containing foo is: 0

, when the last known value of the $size variable is 855, but the first script gets it right? Why should they be any different?

Your help with this would be greatly appreciated, as I am just new to learning shell scripting, and I would like to know why they are producing different results.

Thanks!

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Join Date: Dec 2006

Posts: 2,030

Reputation: Aia has much to be proud of

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Aia

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Postaholic

Re: For loop not bringing variable back properly

Feb 9th, 2009

>Basically, I want to know why the second script returns the line:
> Total size of files containing foo is: 0
Variable scope problem in the while loop with | (pipe)
More here.

Last edited by Aia; Feb 9th, 2009 at 10:43 pm.

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Join Date: Oct 2007

Posts: 399

Reputation: eggi will become famous soon enough

Solved Threads: 47

eggi

Offline

Posting Whiz

Re: For loop not bringing variable back properly

Feb 9th, 2009

Hey there,

Just in case you have to do it the second way, this form works in bash 3.x (possibly earlier versions) and avoids the variable scoping problem while maintaining the integrity of the command you were feeding to the pipe.

 Help with Code Tags 
 Shell Scripting Syntax (Toggle Plain Text) 
while read j1 j2 j3 j4 fsize j5 j6 j7 fname 
do
	[ ! -f $fname ] && continue
 
	if grep $pattern "$fname" > /dev/null 2>%1
	then
		total=`expr $total + $fsize`
		echo "size is: $total"
	fi
done <<< "`ls -l`"
echo "Total size of files containing $pattern is: $total"
while read j1 j2 j3 j4 fsize j5 j6 j7 fname 
do
	[ ! -f $fname ] && continue

	if grep $pattern "$fname" > /dev/null 2>%1
	then
		total=`expr $total + $fsize`
		echo "size is: $total"
	fi
done <<< "`ls -l`"
echo "Total size of files containing $pattern is: $total"

hope it helps

, Mike

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Join Date: Sep 2008

Posts: 2

Reputation: gornhorse is an unknown quantity at this point

Solved Threads: 0

gornhorse

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Newbie Poster

Re: For loop not bringing variable back properly

Feb 11th, 2009

Thanks for that!

I used the 3rd option that is sh-compliant, with the fix of putting the last echo inside the } bracket.

I didn't realise there was an issue with ammending the variable value that was set outside the loop - it's not anywhere in my training! So, at least i've learned from my mistake!

Thanks very much for your help - greatly appreciated.