#!/usr/bin/perl -w
{
open A,shift;   

foreach (<A>)   
{$a{$_}++};     
               
open B,shift;  
foreach (<B>)
{$b{$_}++};  

open C,shift
foreach(<C>)
{
print unless $a{$_}
print unless $b{$_} 
}
}    

my ($file1, $file2) = @ARGV;

open (FILE1, $file1) or die "Can't open $file1: $!\n";
open (FILE2, $file2) or die "Can't open $file2: $!\n";
open (MERGE, ">merged") or die "Can't open merged file: $!\n";

my $line1 = <FILE1>;  
my $line2 = <FILE2>;

while (defined ($line1) || defined ($line2)) {
     if ($line1 =~ /^\#(\d+)\s+/) {
        $tmp=$1;
$line1=<FILE1>;
     }

     if ($line1 =~ /^[io]\d+/){
          print MERGE $line1;
          $line1 = <FILE1>;
          next;
     }  

     @array= split /\s/, $line2;
     $last= $array[$#array];  
      if ($last !=  $tmp) {
         $line2 =<FILE2>;
         next;
     }
     else {
print MERGE $line2;
         $line2=<FILE2>;
     }
} 

use strict;
use warnings;
 
use FileHandle;
 
# input files
my $fh1 = FileHandle->new('f1.txt') or die "ERROR: $!";
my $fh2 = FileHandle->new('f2.txt') or die "ERROR: $!";
 
# output file
my $fh3 = FileHandle->new(">f3.txt") or die "ERROR: $!";
 
while (!$fh1->eof() || !$fh2->eof()){
		my $l1 = $fh1->getline() if (!$fh1->eof()); 
		my $l2 = $fh2->getline() if (!$fh2->eof());
 
		if ( (defined $l1) && (defined $l2)){
				if ($l1 ne $l2){
						$fh3->print($l1);
						$fh3->print($l2);	
				}
		}
		else{
				$fh3->print("\n".$l1) if (defined $l1);
				$fh3->print("\n".$l2) if (defined $l2);
		}
}
 
$fh1->close();
$fh2->close();
$fh3->close();

use strict;
use warnings;
 
use FileHandle;
 
# input files
my $fh1 = FileHandle->new('f1.txt') or die "ERROR: $!";
my $fh2 = FileHandle->new('f2.txt') or die "ERROR: $!";
 
# output file
my $fh3 = FileHandle->new(">f3.txt") or die "ERROR: $!";
 
while (!$fh1->eof() || !$fh2->eof()){
		my $l1 = $fh1->getline() if (!$fh1->eof()); 
		my $l2 = $fh2->getline() if (!$fh2->eof());
 
		if ( (defined $l1) && (defined $l2)){
				my @al1 = split(' ', $l1);
				my @al2 = split(' ', $l2);
 
				if ($al1[0] ne $al2[0]){
						$fh3->print($l1);
						$fh3->print($l2);	
				}
				else{
						$fh3->print($l1);				# add any one line from either of the file, to make sure we have every unique line from two file
				}
		}
		else{
				# add extra lines of files
				$fh3->print("\n".$l1) if (defined $l1);
				$fh3->print("\n".$l2) if (defined $l2);
		}
}
 
$fh1->close();
$fh2->close();
$fh3->close();

#f1.txt
name1 account1 123
name2 account2 324
name3 account3 345
name4 account3 345
name6 account3 345
------------------------
#f2.txt
name1 account1 123
name2 account4 324
name5 account3 345
-----------------------
#OUTPUT: f3.txt
name1 account1 123
name2 account2 324
name3 account3 345
name5 account3 345

name4 account3 345

name6 account3 345