@files = qw(model1bbb model2ccc model3i moduuu);
PREF: for my $i (0..length($files[0])-1) {
my $substr = substr($files[0], 0, $i+1);
(/^$substr/ or ((print 'Pref', substr($files[0], 0, $i)), last PREF)) for (@files[1..$#files]);
}