I like to make that of further use without having to edit the source each time, so I added a bit at it:

print 'Enter folder for renaming: ';
    chomp(my $dir=<STDIN>);
print 'rename from *.';
    chomp(my $from=<STDIN>);
print 'rename to *.';
    chomp(my $to=<STDIN>);

$dir .= '/' unless ($dir =~ /[\/]$/);

while (<$dir*.$from>) {
    my ($old,$new);
    $old = $new = $_;
    $new =~ s/$from$/$to/;
    rename $old, $new;
}
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