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 output should be like this :

1
2
0
6

How can I do it ?

Answer 1

Just to make it shorter ...

% awk 'NR>1{print $1-p} {p=$1}' file
1
2
0
6

Answer 2

Try the following code :

awk '
    NR == 1{old = $1; next}     # if 1st line 
    {print $1 - old; old = $1}  # else...
' file.txt
1
2
0
6

explanations

• NR is the ordinal number of the current record from the start of input. Inside a BEGIN action the value shall be zero. Inside an END action the value shall be the number of the last record processed.
• next statement shall cause all further processing of the current input record to be abandoned. The behavior is undefined if a next statement appears or is invoked in a BEGIN or END action.

Answer 3

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