#!/usr/bin/env ruby
#supress any warning when calling other shell commands.
$VERBOSE = nil

def die(msg)
        puts msg
        exit 1
end

$cmd = ARGV.shift
die "you should specify a string of ruby code to deal with eachline of STDIN" unless $cmd

$in = STDIN.readlines
$in.each do |x|
        x.chomp!
        eval($cmd)
end

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?

do sth. on eachline from STDIN

Ruby