"awk" doubt- do reply

Hi

I am new to this shell scripting.
how to get the line by line fields in a for loop.

for eg(my script):

line=0
for s in `cat system`
do
line=`expr $line + 1`
a=`awk -F' ' 'NR=$line{print $7}' sample`
done

this is my script where I get a syntax error.
my error: is Field $() is not correct.
The input line number is 1. The file is samp.
The source line number is 1.

can anyone help me.