The script includes a print statement for this purpose. The print statement prints the contents of $link correctly, but system("echo", $link) only prints w. If you download the sample file I included and put it in the same directory of the script you can see the result yourself.
Comment on Re^2: system function not handling string properly
What is your OS? What shows 'which echo' on your system?
This code works pretty well on my system:
#!/usr/bin/env perl
use strict;
use warnings;
use 5.010;
my $url = '"www.youtube.com/watch?v=mark"';
system('echo', $url);
$url = "www.youtube.com/watch?v=mark";
system('echo', $url);