read line in a for loop

balajim · #1 (**permalink**) 10-28-2008

Hi All,
How can we use read line using the index value of a FOR loop?
eg:
pt_mstr,pt_status,8
pt_mstr,pt_buyer,8
pt_mstr,pt_sfty_stk,8
pt_mstr,pt_ord_pol,3
pt_mstr,pt_capacity,8
pt_mstr,pt_plan_ord,3
pt_mstr,pt_ord_mult,8

From this file i want to read the line2, 3 and 4 only using a FOR Loop.

for (( i=2; $i <= 4; i++ ))
do
read line
echo $line
done

This will read 3 lines from the top, but what i want is the lines from the index of the FOR Loop. Here the index of the for loop is 2, 3 and 4 so i want the line2 , 3 and 4

Thanks,
Balaji

joeyg · #2 (**permalink**) 10-28-2008

I would probably approach with head and tail command.

Code:

> tail +2 file14 | head -3
pt_mstr,pt_buyer,8
pt_mstr,pt_sfty_stk,8
pt_mstr,pt_ord_pol,3

fpmurphy · #3 (**permalink**) 10-28-2008

You cannot easily do what you want using a for loop since there is no connection between your i variable and read. read does not magically advance to the i th line!

Here is a simple way to achieve what you want use a while loop

Code:

#/bin/bash

i=0
while read line
do
   (( ++i ))
   case $i in
    [2-4]) echo $line
   esac
done < file

lifegeek · #4 (**permalink**) 10-29-2008

file.txt
--------------------------------
pt_mstr,pt_status,8
pt_mstr,pt_buyer,8
pt_mstr,pt_sfty_stk,8
pt_mstr,pt_ord_pol,3
pt_mstr,pt_capacity,8
pt_mstr,pt_plan_ord,3
pt_mstr,pt_ord_mult,8
---------------------------------

Code:

#! /bin/bash 

set $(cat file.txt)
for (( i=2; $i <= 4; i++ ))
do
eval echo \$$i
done

or

Code:

#! /bin/bash

for i in `cat`
do
((j++))
if [ $j -eq 2 -o $j -eq 3 -o $j -eq 4 ]
then
echo $i
fi
done

or

Code:

cat >> temp && sed -n '2,4p' temp

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