$filename = 'OUT';
$max = 100;

my ($fname, $ext) = split(/\./, $filename, 2);
$ext = '.' . $ext if ($ext); my @temp;
for (my $i = 1; $i <= $max; $i++) {
    if (!open(IN, "$fname$i$ext")) { print "Can't open $fname$i$ext for read.<br>\n"; }
    else {
        @temp = <IN>;
        close(IN);
    
        # Do whatever editing is necessary on file data... 

        if (!open(OUT, ">$fname$i$ext")) { print "Can't open $fname$i$ext for write.<br>\n"; }
        else {
            print OUT @temp;
            close(OUT);
        }
    }
}