I hacked this piece of code together. It may work for you or it may not. I think it is pretty straightforward, except for the two-level Schwartzian transform-like anonymous array nesting (Data::Dumper should help, though)...

#!perl 

use strict;
use warnings;

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

@query = sort { $a->[1] <=> $b->[1] || $a->[2] <=> $b->[2] }
         grep { $_->[1] > -1 }
         map  { [$_, index($string, $_), index($string, $_) + length($
+_) - 1] }
         @query;
         
my @matches;

@query
   or die "No matches";
   
my $i = -1;
my $p = -2;

for (@query) {
   if ($p + 1 < $_->[1]) {
      ++$i;
   }
   push @{$matches[$i]}, $_;
   $p = $_->[2];
}

@matches = sort { $b->[0] <=> $a->[0] }
           map  { [$_->[-1]->[2] - $_->[0]->[1] + 1, $_] }
           @matches;
           
print "Longest continuous match has length $matches[0]->[0]\n\n";
print "$string\n";
for (@{$matches[0]->[1]}) {
   print ' ' x $_->[1] . $_->[0] . "\n";
}
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