#!/usr/bin/perl -w
use strict;

my %fixers=(
    'amazon.com' => 'danube.com',
    'ibm.com'    => 'bm.com',
    );

my $text = qq(
Blah <a href="http://amazon.com/foo">one</a>
     <a href="http://ebay.com/foo">two</a>
);

map {
  $text =~ s/$_/$fixers{$_}/;
}keys %fixers;

print $text;