difference between number in the same column using AWK

Question

I have a file containing one column of number:

1
2
4
4
10

I would like to calculate the difference between each number using awk. The outpu

Answer 1

In case awk is not a strict requirement, a shell solution:

set -- $(< file)
p=$1; shift; while (($# > 0)); do echo $(($1 - p)); p=$1; shift; done

DRYer

set -- $(< file)
while (($#>0)); do [[ -n $p ]] && echo $(($1-p)); p=$1; shift; done