#! perl -slw
use strict;
use List::Util qw[ reduce ];

sub longestComposite{
	my( $string, $qRef ) = @_;
	my $copy = ' ' x length $string;

	$string =~ s[($_)]{
		my $len = length $1;
		substr( $copy, pos( $string ), $len ) = $1;
		$1;
	}ge for @$qRef;

	return reduce{ 
          length $a > length $b ? $a : $b 
    } split ' ', $copy;
}

my $string ="EICHENBAUMSCHULE";
my @query = qw( EIC BAUM UMS CHU LE );

print longestComposite( $string, \@query );

__END__
P:\test>366569
BAUMSCHULE