use strict;
use warnings; # this is also useful

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

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

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