[aaaa@bbbb] $ cat a.txt
ddddddddddddddddd ffffffffffffffffffffffffff dddddddddddddddddddddddddddd ssssssssssssssssssssssssssss ggggggggggggggggggggggggg dddddddddddddddddddddd fffffffffffffffffffffffff ddddddddddddddddddddddddddd sssssssssssssssssssssssss fffffffffffffffffffffffff ssssssssssssssssssssssssssss ffffffffffffffffffff vvvvvvvvvvvvvvvvvvvvvvvvvvvv xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb ssssssssssssssssssssssssssssssssss dddddddddddddddddddddddddddddddddddddd eeeeeeeeeeeeeeeeeeeeeeeeee ccccccccccccccccccccccc



b=`grep f a.txt`
start_pos=0
increment=100
counter=1
while(true)
do
print_line=`echo $b | cut -c$start_pos-$increment`
start_pos=`expr $start_pos + 100`
increment=`expr $start_pos + 100`
if [ -z "$print_line" ]
then
break
fi
echo $counter " " $print_line
counter=`expr $counter + 1`
done




O/p:


1 ddddddddddddddddd ffffffffffffffffffffffffff dddddddddddddddddddddddddddd ssssssssssssssssssssssssss
2 sss ggggggggggggggggggggggggg dddddddddddddddddddddd fffffffffffffffffffffffff dddddddddddddddddddddd
3 dddddd sssssssssssssssssssssssss fffffffffffffffffffffffff ssssssssssssssssssssssssssss fffffffffffff
4 ffffffff vvvvvvvvvvvvvvvvvvvvvvvvvvvv xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
5 b ssssssssssssssssssssssssssssssssss dddddddddddddddddddddddddddddddddddddd eeeeeeeeeeeeeeeeeeeeeeeee
6 ee ccccccccccccccccccccccc

---------- Post updated at 07:27 AM ---------- Previous update was at 07:21 AM ----------

If you want complete words, you can use the field separator:

b=`grep f a.txt`
start_pos=1
increment=4
counter=1
while(true)
do
print_line=`echo $b | cut -d " " -f$start_pos-$increment`
start_pos=`expr $start_pos + 4`
increment=`expr $start_pos + 4`
if [ -z "$print_line" ]
then
break
fi
echo $counter " " $print_line
counter=`expr $counter + 1`
done