difference between number in the same column using AWK command

Question

I have a file containing one column of number:

1
2
4
7
10
12

and i want output like below

1
3
2

e.g I need difference of each two iteration.

like 2-1=1 , 7-4=3, 12-10=2

Answer 1

awk 'NR%2{x=$0;next}{print $0-x}' File

For the odd lines, save the line (number) to variable x. For even lines, print the difference using previously saved x