The following code will split each line that begins with one or more digits, assuming the elements are separated by spaces.

my $file = <STDIN>;
chomp($file);

if ($file =~ /\w+\.dat/) {
   open(DATOS, "$file") or die "error message";
   while (<DATOS>) {
      push(@lines, $_) if /^\d/;
   }
   close DATOS;
   foreach my $line (@lines) {
       my @fields = split(/\s+/, $line);
       print "@fields";   # or whatever else you want to do
   }
}
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