I have to use hash(key,value) concept.

TIMTOWTDI and here is a counter-example.

use strict;
use warnings;
use Test::More tests => 1;

my $in = <<EOIN;
# this is a new file
{
date 14/07/2016
time 11:15  
end 11:20   
total 30    
No  "FRUITS"

Fruit_Class
    {
    Name    "fruit 1"
    fruitName   "apple.fru"
    fruitId "0"         
    fruitCount  5
    fruitValue  6           
    }

    {
    Name    "fruit 2"
    fruitName   "orange.fru"
    fruitId "1"
    fruitCount  10
    fruitValue  20  
    }
}
EOIN

my $want = <<EOWANT;
# this is a new file
{date 14/07/2016
time 11:15  
end 11:20   
total 30    
No  FRUITS

Fruit_Class
    {
    Name    fruit_1
    fruitId 0           
    apple_fru.fruitCount    5
    fruitValue  6           
    }
Fruit_Class
    {
    Name    fruit_2
    fruitId 1
    orange_fru.fruitCount   10
    fruitValue  20  
    }
}
EOWANT

my $name = '';
my $out  = '';
my $nr   = 0;

for (split "\n", $in) {
    tr /"//d;
    s/ (\d)/_$1/ if $nr++ > 5;
    if (/^\s+fruitName\s+(.*?)$/) {
        ($name = $1) =~ s/\./_/;
        next;
    }
    s/fruitCount/$name.fruitCount/;
    s/^$/Fruit_Class/ if $nr > 10;
    if (/^{/) {
        $out .= $_;
        next;
    }
    $out .= "$_\n";
}

is ($out, $want);
[download]

Note that I've removed the arbitrary trailing tabs from both files where they existed before importing. If you need those then it's up to you to implement that part as it is genuinely arbitrary.