use strict;
use warnings;

my (@gsm_site, @umts_site);

while (<DATA>) {
   my ($name1,$lon1,$lat1, $name2,$lon2,$lat2) = split /[\s"]*,["\s]*/
+, $_;
   
    next unless $lat1 and $lon1; # Avoid title lines
    push @gsm_site, {NAME=>$name1, LAT=>$lat1, LON=>$lon1};   
    push @umts_site,{NAME=>$name2, LAT=>$lat2, LON=>$lon2};
}

for my $g (@gsm_site){
      $g->{NEAREST}         =  $umts_site[0]; # Initial assumption til
+l we know better
      $g->{DIST_TO_NEAREST} = distance($g->{LAT},$g->{LON}, $g->{NEARE
+ST}{LAT},$g->{NEAREST}{LON}, "K");
      for my $u (@umts_site[1..$#umts_site]){
         my $this_distance = distance($g->{LAT},$g->{LON}, $u->{LAT},$
+u->{LON}, "K");
         next unless $this_distance < $g->{DIST_TO_NEAREST};
         $g->{NEAREST} = $u;
         $g->{DIST_TO_NEAREST} = $this_distance;
      }
}

# Print them out
for my $g (@gsm_site){
   print "$g->{NAME}, $g->{NEAREST}->{NAME}, $g->{DIST_TO_NEAREST},\n"
+;
}


__DATA__
NameA Longitude Latitude NameB Longitude Latitude 
10001_NI0001, 36.79887354, -1.26122956, " WL3762", 34.52328889 , -1.00
+7941667
NI0006, 36.86998613, -1.295393144, " NM5286", 36.83137418, -1.17262637
+2
NI0066, 36.82748524, -1.25734101, " EC4140", 37.4580536, -0.53351668,
[download]

Thank you Monks, for your great help. I did try NetWallah's code,thanks O great Abbot. I am however getting some errors originating from the subroutine which am sharing here as you had suggested. I previously got such errors while trying different loops but avoided tinkering with the subroutine which works as it is. What should i change in the new code? Here are the exceptions am getting and the subroutine code;

The errors, the line 5852 is the last line in my CSV file
C:\MyScripts\2G3Gdistance.pl
Argument "Longitude" isn't numeric in subtraction (-) at
C:\MyScripts\2G3Gdistance.pl line 53, <COMBINED> line 5852 (#1)
Argument "Latitude" isn't numeric in multiplication (*) at
C:\MyScripts\2G3Gdistance.pl line 80, <COMBINED> line 5852 (#1)
Use of uninitialized value $lon2 in subtraction (-) at
C:\MyScripts\2G3Gdistance.pl line 53, <COMBINED> line 5852 (#2)
(W uninitialized) An undefined value was used as if it were already
defined. It was interpreted as a "" or a 0, but maybe it was a mistake.
To suppress this warning assign a defined value to your variables.
Use of uninitialized value $deg in multiplication (*) at
C:\MyScripts\2G3Gdistance.pl line 80, <COMBINED> line 5852 (#2)
Uncaught exception from user code:
Can't take sqrt of -4.44089e-016 at C:\MyScripts\2G3Gdistance.pl line 71, <COMBINED> line 5852.
main::acos(1) called at C:\MyScripts\2G3Gdistance.pl line 55
main::distance(-0.433525648, 36.968599085, -0.433525648, 36.96859909, "K") called at C:\MyVolume\Development\MyScripts\2G3Gdistance.pl line 150


The subroutine code

 my $pi = atan2(1,1) * 4;

sub distance {
    my ($lat1, $lon1, $lat2, $lon2, $unit) = @_;
    my $theta = $lon1 - $lon2;
    my $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) + cos(deg2rad
+($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
  $dist  = acos($dist);
  $dist = rad2deg($dist);
  $dist = $dist * 60 * 1.1515;
  if ($unit eq "K") {
      $dist = $dist * 1.609344;
  } elsif ($unit eq "N") {
      $dist = $dist * 0.8684;
        }
    return ($dist);
}

#:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+:
#:::  This function get the arccos function using arctan function   ::
+:
#:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+:
sub acos {
    my ($rad) = @_;
    my $ret = atan2(sqrt(1 - $rad**2), $rad);
    return $ret;
}

#:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+:
#:::  This function converts decimal degrees to radians             ::
+:
#:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+:
sub deg2rad {
    my ($deg) = @_;
    return ($deg * $pi / 180);
}

#:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+:
#:::  This function converts radians to decimal degrees             ::
+:
#:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
+:
sub rad2deg {
    my ($rad) = @_;
    return ($rad * 180 / $pi);

}

print distance(32.9697, -96.80322, 29.46786, -98.53506, "K") . " Kilom
+eters\n";
[download]

Argument "Longitude" isn't numeric in subtraction (-) at C:\MyScripts\
+2G3Gdistance.pl line 53, <COMBINED> line 5852 (#1)
Argument "Latitude" isn't numeric in multiplication (*) at C:\MyScript
+s\2G3Gdistance.pl line 80, <COMBINED> line 5852 (#1)
[download]

These are clearly the results of you trying to perform arithmetic on the values obtained from your data file's header row. Don't do that. Only start processing the actual data from row 2 onwards.

Use of uninitialized value $lon2 in subtraction (-) at C:\MyScripts\2G3Gdistance.pl line 53, <COMBINED> line 5852 (#2)

This suggests that you have not parsed the data file correctly because $lon2 remains undefined. I suggest that you print out the values of all the arguments to distance() as soon as you retrieve them in order to determine how the parsing has failed and then correct that. The later errors are likely propagations of this problem.

Do take a look through the Basic debugging checklist if you have not already done so. It will help you clear up such similar problems in future.

Here's where am stuck, how do I loop the first item on NameA column to iterate over all NameBs and return the smallest distance, together with both corresponding NameA and NameB entries then move to the next row and repeat above, and so on till end of file.

What does that mean?

?"Loop first item"? What distance?

If you could please use the numbers from the three lines of data you posted, and in pencil-and-paper fashion , solve the problem step by step for those three lines, this would help me understand what you're asking

Its hard to interpret a program that doesn't work to understand the question being asked

Probably need to read the file into a hash of arrays first, then query it like a database, do some calculations ...

http://perlmaven.com/perl-split from split perl for simple examples of how to use split.