@ARGV = glob 'datafile*';

open my $OUTPUT, '>', 'output_file' or die "Cannot open 'output_file' because: $!";

while ( <> ) {
    if ( $. == 1 ) {
        print $OUTPUT $ARGV =~ /(\d+)$/, " has";
        }
    print $OUTPUT " ", ( split )[ 2 ];
    if ( eof ) {
        print $OUTPUT " $. columns\n";
        close ARGV;
        }
    }