Shell Programming and Scripting

for i in `cat abc.txt`
do
  echo $i // this will display first line
  i=$i+1;  // this doesnt work for me. 
  echo $i; //this will display secound line
done

12
123
1234
12345
123
1234

Item1 apple:
a=12
b=123
Item2 banana:
a=1234
b=12345
Item3 soda:

for i in `cat first list`
do
  echo $i
  for j in `cat 2ndlist.txt` 
    for k in `cat 3rdlist.txt`
      echo $j $k $k
    done
  done
done

i=$((i+1))

let i=i+1

cat abc.txt | while read line
do
          echo "${line}"          # Display line
done

cat abc.txt | while read line
do
          echo "${line}"          # Display first line and every odd-numbered line
          read line                  # Read even numbered lines
          echo "${line}"           # Display 2nd line and every even-numbered line
done