#! /usr/bin/perl/ -w

use strict;

my @strings = qw ( cooling rooting hooting looking doormat );

our @common_letters;

my $reference = shift @strings;

() = $reference =~ /(.)(?{	
				my $letter = $1; 
				my $position = $-[0]; 
			   	my $bolean = 1; 
			  	
				for ( @strings ) 
				{ 
					if ( substr( $_, $position, 1 ) ne $letter )
					{ 
						$bolean = 0; 
						last
					} 
				}
				
				$common_letters[ $position ] = $letter if ( $bolean ); 
			})/gx;

print ( $common_letters[ $_ ] || "-" ) for ( 0 .. length $reference );