need a recursion? well then do it:

#!/usr/bin/env perl

use warnings;
use strict;

my $curUrl = "http://localhost:8080";
my $tarUrl = "http://localhost";

my @buf;

my ($line, $f);

sub diveinto {

    print "dive into: $_[0]\n";
    opendir DIR, $_[0] or die "Could not open directory";
    my @files = readdir DIR;
    closedir DIR;

    foreach $f (@files) {
        if ($f =~ /\.{1,2}/) {next }
        print "processing: $f\n";
        if ( -d "$_[0]/$f" ) { diveinto ("$_[0]/$f") }
        else {
            open FILE, "<". "$_[0]/$f" or die "Could not open file -- 
+$_[0]/$f";
            @buf = <FILE>;
            close FILE;

            open W, ">" . "$_[0]/$f" or die "cunt open for r/w -- $_[0
+]/$f";
            foreach $line (@buf) {
                $line =~ s/$curUrl/$tarUrl/g and print "Yes";
                print W $line;
            }
            close W;
        }
    }

}

diveinto $ARGV[0];
[download]

* I leave debug 'print'-s as is to help you understand what it does. It can be shrinked twice in size.
* If it is a directory, we just call ourselves recursively
* The original loop where you trying to replace string need to write result of s///;