use strict;
my $str = "the boy walked the dog";
$str=ChainSubs($str,
	       walked=>'fed',
	       boy=>'girl',
	       dog=>'Audrey II'
	      );
print $str;

sub ChainSubs{
  my ($string,%subs)=@_;
  foreach my $original (keys %subs) {
    $string=~s/$original/$subs{$original}/;
  }
  $string;
}