use File::Find qw( find );

my @desired_files = `cat list_o_dirs`;
my %desired_files;
@desired_files{ map lc, @desired_files } = (1) x @desired_files;

my @hits;
find( $root_dir, sub {
      push @hits, $File::Find::name if exists $desired_files{ lc $File::Find::name }
    );