I'm processing some data an printing the results to a file. The data is taking me several days to process and I want to 'cat' the file periodically to check that file contents are okay.

I'm using 'open' to write to the file but I'm not seeing any data in the file when I know there should be. I know I'm getting the correct output because when I print to the screen and not the file, I see all the data without a problem.

As far as I understand "open" just does buffered write. Is this why I'm not seeing any data in my file yet?

Is there a way to unbuffer open?

Is syswrite the only way to do an unbuffered write?

Here's my code, I'm comparing each gps point in one file to each gps point in a second file. I'm saving each set of file points that are within 1000 feet to a file. 
#!/usr/bin/perl -w

use Geo::Distance;
use Text::CSV_XS;

my $geo = new Geo::Distance;

open FIRST, "</gps/gpspoints.csv" or die "Couldn't open: $!";

my  $csv = Text::CSV_XS->new({
     'quote_char'  => '"',
     'escape_char' => '"',
     'sep_char'    => ','
         });

open(DAT,">/gps/datapoints.csv") || die("Cannot Open File");

while( my $first_file_line = <FIRST>){
  if ($csv->parse($first_file_line)) {    .
        my ($lon2, $lat2) = $csv->fields;

open SECOND, "</gps/newdataponts.csv" or die "Couldn't open: $!";
while( my $second_file_line = <SECOND>){

if ($csv->parse($second_file_line)) {
($lat, $lon) = $csv->fields;

$distance = $geo->distance( 'foot', $lon,$lat => $lon2,$lat2 );

if ( $distance < 1000 ) {
print DAT "$lat2, $lon2, $lat, $lon, $distance \r\n";
}

}}

close SECOND;

  } else {
    my $err = $csv->error_input;
    print "parse() failed on argument: ", $err, "\n";
  }
 }


close FIRST;
close DAT;

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In reply to open - Unbuffered Write??? by awohld

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