Update: OP changed the question completely, so now my reply only makes limited sense.

Most of the perl monks who read your question are pretty good at Perl, but know next to nothing at about biology. So if you want helpful replies, you should explain what you mean with

Generate given Length random intervals from Genome data

in a way that doesn't require prior biology knowledge. And you also need to explain how that should lead to the expected output.

Also we don't know what length.pl does, so we can't even try to run your program.

Have you seen the ever popular BioPerl site? They might be able to help better than the Monks, since Bioinformatics is the specialization of the site.

This may help you

use strict;
use warnings;

my %rangeFile; ## hash
my %geneomeFile;

## From the Range Data File
open my $IN2, "RangeFile.txt" or die $!
while(<$IN1>){
    chomp($_);
    $rangeFile{$_} =  1;
}
close($IN1);

## From Genome Data 
open my $IN2, "GenomeFile.txt" or die $!
while(<$IN2>){
    chomp($_);
        my @line = split('\t', $_); ## considering if genome data is t
+ab-del file
    $genomeFile{$_} =  1;
}
close($IN2);

## Randomly Choosing Name from Genome Data
foreach (rand keys %hash){
#### Code for step 3 ###
}
[download]

Btw, I didnt understan your step 3.