use strict;
my @varlist = ("foo", "bar", "baz");
my ($foo, $bar, $baz) = ("1", "2", "3");
my $newfoo = "A";


foreach my $var (@varlist) {

  my $newvarname = "new" . $var;

  if (defined $$newvarname) {

    $$var = $$newvarname;
    
  }

}