This script is intended to use after the pipe '|' on unix shell. It execute a one-line ruby code(you can split multi-line ruby-code with ';', of course) iteratively on each-line from the STDIN, each-line of which is assigned to a variable x.

eg.
ls | eachline.rb '$no||=1;puts "#$no - #{x}";$no+=1'
the output looks like this:
1 - README.image
2 - README.image~
3 - bin
4 - boot
...

Simple enough, isn't it?