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Old 06-09-2008, 02:39 PM   #1
pdklinux79
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Registered: Jun 2008
Posts: 29

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working with variables- how?


hi i am working in bash.

few lines of code is :
1.num=1

2.grep '^ID' vdat.txt | while read line
3.do
4.field_3=$(echo "$line" | awk '{print $3}')
5.echo $field_3
6.array[$num]=$field_3
7.echo ${array[$num]}
8.num=`expr $num + 1`
9.done
10.echo $num

the value of num at line 10 is 1 even after manipulating it in the line 8 inside for loop.. lets say it is a for loop with i=1, i<=4 i++ and i manipulate the value of num inside the forloop.

how can get the value of num as 4 outside the loop?

im having problem as the num inside the loop becomes local and doesnt effact the global variable

am a newbie.. please help me.
 
Old 06-09-2008, 03:10 PM   #2
Uncle_Theodore
Member
 
Registered: Dec 2007
Location: Charleston WV, USA
Distribution: Slackware 12.2, Arch Linux Amd64
Posts: 896

Rep: Reputation: 60
Quote:
Originally Posted by pdklinux79 View Post
hi i am working in bash.

few lines of code is :
1.num=1

2.grep '^ID' vdat.txt | while read line
3.do
4.field_3=$(echo "$line" | awk '{print $3}')
5.echo $field_3
6.array[$num]=$field_3
7.echo ${array[$num]}
8.num=`expr $num + 1`
9.done
10.echo $num

the value of num at line 10 is 1 even after manipulating it in the line 8 inside for loop.. lets say it is a for loop with i=1, i<=4 i++ and i manipulate the value of num inside the forloop.

how can get the value of num as 4 outside the loop?

im having problem as the num inside the loop becomes local and doesnt effact the global variable

am a newbie.. please help me.
OK, the problem is that when you use a pipe, bash forks out a subshell which performs your while loop. Variables, including your $num are specific to that subshell and when the loop is finished, you see the original $num that has never been modified.

On a side note, this line num=`expr $num + 1` seems strange. Do you mean something like num=$((num+1)) ?
 
Old 06-09-2008, 03:27 PM   #3
pdklinux79
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Registered: Jun 2008
Posts: 29

Original Poster
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yes.. it is num= num+1..

so how do i get the effect i want?is there any way?
 
Old 06-09-2008, 03:35 PM   #4
Uncle_Theodore
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Registered: Dec 2007
Location: Charleston WV, USA
Distribution: Slackware 12.2, Arch Linux Amd64
Posts: 896

Rep: Reputation: 60
Quote:
Originally Posted by pdklinux79 View Post
yes.. it is num= num+1..

so how do i get the effect i want?is there any way?
Well, grep the file without a pipe. Something like this

Code:
1.num=1

2.while read line
3.do
4.field_3=$(echo "$line" | awk '{print $3}')
5.echo $field_3
6.array[$num]=$field_3
7.echo ${array[$num]}
8.num=$((num+1))
9.done < <(grep '^ID' vdat.txt)
10.echo $num
should do it.
 
Old 06-09-2008, 03:51 PM   #5
pdklinux79
LQ Newbie
 
Registered: Jun 2008
Posts: 29

Original Poster
Rep: Reputation: 15
Thank you Uncle Theodre so much.. it is working..
 
Old 06-10-2008, 05:50 AM   #6
CanOfPoke
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Registered: Jun 2008
Posts: 3

Rep: Reputation: 0
I had same problem it all works fine now though.
 
  


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