In a simple webapp I need to map URLs to filenames or filepaths.

This app has a requirement that it can depend only on modules in the core Perl ditribution (5.6.0 and later). The problem is that filename length on most filesystems is limited to 255. Another limit is about 32k subdirectories in a single folder.

My solution:

my $filename = $url;

if (length($filename) > $MAXPATHLEN) { # if filename longer than 255
    my $part1 = substr($filename, 0, $MAXPATHLEN - 13);        # first 242 chars
    my $part2 = crypt(0, substr($filename, $MAXPATHLEN - 13)); # 13 chars hash
    $filename = $part1.$part2;
}
$filename =~ s!/!_!g; # escape directory separator

Is it reliable ? How can it be improved ?