perl - compute difference of number in file using perldo -

i have file 2 numbers

4     4 4      4 9         8 7     7

each line may have different number of spaces. use perldo compute difference of 2 numbers:

i trying right now

:perldo @a=split(/ +/, $_); $_ =  $a[0] - $a[1]

i think should work file not changed @ all.

how can using perldo?

i don't know perl, works here:

:perldo @a=split(/ +/, $_); $_ =  $a[0] - $a[1]; print $_

since editing file in vim, consider in vim way:

:%s/\v(\d+)\s*(\d+)/\=submatch(2)-submatch(1)

KHS