one
two
three

##</code><code>##

filterTwoThree.pl | oneTwoThree.pl

##</code><code>##

two 
three

##</code><code>##

#!c:/perl/bin/perl
#oneTwoThree.pl
use warnings;
use strict;

print "one\n";
print "two\n";
print "three\n";

##</code><code>##

#filterTwoAndThree.pl
use warnings;
use strict;

if (/two|three/) {
  print $_;
}

##</code><code>##

perl oneTwoThree.pl | perl -n filterTwoAndThree.pl