I am trying to run the code what you have mentioned.
But this is resulting in "List form of pipe open not implemented at...
+sort.pl line 19"(on my windows system).I came to know that "List form
+ of pipe open "is not supported on windows system. and I changed it t
+o 
open $fh, "|sort $filename", or die;
 and the entire code looks like this:

use strict;
use warnings;

    
my $filename = "sort_input";
my $fh;
my $line;
my $key;
my $value;
my $prev_key;
my $prev_value;
my $file_consolidated_sort= "sort_output";
my $FH_sorting;



#open $fh, '-|', 'sort', $filename or die;


open $FH_sorting, ">>$file_consolidated_sort" or die "$!";

open $fh, "|sort $filename", or die;

chomp( $line = <$fh> );
 ($prev_key, $prev_value) = split /,,/, $line;
while (<$fh>) {
  chomp;
   ($key, $value) = split /,,/;
  if ($prev_key eq $key) {
    $prev_value .= $value;
  }
  else {
    print $FH_sorting $prev_key ,, $prev_value;
    
    ($prev_key, $prev_value) = ($key, $value);
  }
}
print $FH_sorting $prev_key,,$prev_value;


close $fh;
close $FH_sorting;

Another point is that I am not able to write the resulted output to th
+e output file handler.All sorted output is getting printed on the scr
+een itself with the warning/error on screen "Use of uninitialized val
+ue $line in chomp at line 25, 26 etc".
I have not tried sorting with huge file(3GB) which is my actual requir
+ement and have not tested for performance will improve or not.

Parelelly I am looking into external sort
[download]

open $fh, "|sort $filename", or die;
[download]

open $fh, "sort $filename |" or die;
[download]