[8/29/2013 7:16:45 AM] User abc def [DEFAULT]
[8/29/2013 7:16:45 AM] User xyz abc [DEFAULT]

##</code><code>##

[8/29/2013<tab>7:16:45<tab>AM] User abc def [DEFAULT]
[8/29/2013<tab>7:16:45<tab>AM] User xyz abc [DEFAULT]

##</code><code>##

#!/usr/bin/perl -w

use strict;


open(FILE, "<input.txt") || die "File not found";
my @lines = <FILE>;
close(FILE);

my @newlines;
foreach(@lines) {

$_ =~ s/\s+/\t/g;
push(@newlines,"$_\n");
  
}
my $file = "output.txt";
unlink $file;
open(FILE, '>>',$file) || die "FILE not found";
print FILE @newlines;

close(FILE);
print "Done \n";

input.txt: 
[8/29/2013 7:16:45 AM] User abc def [DEFAULT]
[8/29/2013 7:16:45 AM] User xyz abc [DEFAULT]

output.txt: with my code
[8/29/2013<tab>7:16:45<tab>AM]<tab>User<tab>abc<tab>def<tab>[DEFAULT]
[8/29/2013<tab>7:16:45<tab>AM]<tab>User<tab>xyz<tab>abc<tab>[DEFAULT]

Output.txt:(expected)
[8/29/2013<tab>7:16:45<tab>AM] User abc def [DEFAULT]
[8/29/2013<tab>7:16:45<tab>AM] User xyz abc [DEFAULT]