For a generic solution to this type of problem you can use Larry Wall's rename.pl script from chapter 9 of the Perl Cookbook-

#!/usr/bin/perl -w
# rename - Larry's filename fixer
$op = shift or die "Usage: rename expr [files]\n";
chomp(@ARGV = <STDIN>) unless @ARGV;
for (@ARGV) {
    $was = $_;
    eval $op;
    die $@ if $@;
    rename($was,$_) unless $was eq $_;
}
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So for your example you would do rename.pl s/^new/U/ *.html *.shtml