By outside, I want solutions that does not use Vim's scripting hacks but try to reuse certain basic *ix tools. Inside Vim stuff asks for solutions to get the column-increment with inside stuff such as scripting.

1           1 
1           2 
1           3 
1   --->    4
1           5
1           6
.           .
.           .

Vim has a script that does column-vise icrementing here. It has gathered about 50/50 ups and down, perhaps tasting a bit reinventing-the-wheel. How do you column-increment stuff in Vim without using such script? Then the other question is, how do you column-increment stuff without/outside Vim?

Most elegant, reusable and preferrably-small wins the race!