my $regex = qr{href\s*=\s*".*?"}; ##

##

use strict;
use warnings; # this is also useful

my $regex = qr{href\s*=\s*".*?"};
my $sub = "href=\"#\"";

while(){
    s/$regex/$sub/g;
    print;
}

__DATA__
afjalsdfj href="asfasdfa" afdsas href="akjshfakjsd"
href = "ajsfhaklj"

##

##

use strict;
use warnings;
use HTML::Parser;
use HTML::Entities;

my $html = join '', ;
my $p = HTML::Parser->new(
    default_h => [ sub { print shift }, 'text' ],
    comment_h => [""],
    start_h => [ \&start, 'tag,attr,attrseq,text' ]
);
$p->parse($html);

sub start {
    my ( $tag, $attr, $attrseq, $text ) = @_;
    unless ( exists $attr->{href} ) {
        print $text;
    }
    else {
        $attr->{href} = "#";
        print "<$tag";
        print " $_=\"", encode_entities( $attr->{$_} ), '"' for (@$attrseq);
        print ">";
    }
}

__DATA__

title
link
some text and more